CN118932270A

CN118932270A - Aluminum-coated silicon steel and preparation method, pre-coated steel, and production process of hot-formed components

Info

Publication number: CN118932270A
Application number: CN202411004121.3A
Authority: CN
Inventors: 肖彪; 周焕能; 李翔; 曾松盛; 周屿; 马接力
Original assignee: Valin Arcelormittal Automotive Steel Co ltd
Current assignee: Valin Arcelormittal Automotive Steel Co ltd
Priority date: 2024-05-27
Filing date: 2024-05-27
Publication date: 2024-11-12
Also published as: CN118241143A; CN119061342A; CN118241143B; CN118932269A

Abstract

The present invention provides aluminum-plated silicon steel and a preparation method, pre-coated steel, and a production process for hot-formed components. The aluminum-plated silicon steel includes a pre-plated layer arranged on a steel substrate. The pre-plated layer includes an intermediate layer and an aluminum-silicon coating; the nominal thickness of the aluminum-silicon coating is 10 μm to 33 μm; the aluminum-silicon coating contains 5 to 40% of an Al-Si phase and 0.1 to 15% of an Al-Si-Fe phase, and the dispersion index of the Al-Si phase and the Al-Si-Fe phase in the aluminum-silicon coating is ≥ 0.05. In the above-mentioned aluminum-plated silicon steel, the Al-Si phase and the Al-Si-Fe phase in the aluminum-silicon coating are in an appropriate ratio and a suitable dispersion index, which is conducive to the subsequent production of hot-formed components with smaller grains and a double-layer Al-rich intermetallic compound layer, thereby improving the coating toughness and environmental tolerance of the hot-formed components, reducing their crack sensitivity, and making the hot-formed components also have the advantages of improved hydrogen embrittlement resistance and corrosion resistance.

Description

Aluminum-plated silicon steel and preparation method thereof, precoated steel and production process of hot-formed component

The invention relates to a patent application, which is a divisional application of an invention patent application with the application date of 2024, 5 and 27, the application number of 202410661792.0, the invention name of aluminized silicon steel, a preparation method, precoated steel and a production process of a thermal forming component.

Technical Field

The invention relates to the field of hot forming steel, in particular to aluminized silicon steel, a preparation method thereof, precoated steel and a production process of a hot forming member.

Background

Currently, the strength of commercial hot formed steel has exceeded 1500MPa, and 2000MPa hot formed steel is becoming a hot spot for automotive steel, and these hot formed steel are desired to have higher toughness and better crack resistance sensitivity while pursuing strength. The material strength of collision energy absorption also reaches the 1000MP level. The plating layer of the traditional aluminum-silicon hot forming steel has a typical four-layer structure, namely (a) an inter-diffusion layer; (b) an intermediate; (c) an Al-rich intermetallic layer; (d) a surface layer. The structure can be produced in a wider hot forming austenitizing processing window, so that not only is higher strength obtained, but also the welding performance of the coating is very excellent.

With the increase of the material cost requirements, a type of thin-coating hot forming steel appears on the market, but the coating of the material is unfavorable for the control of a welding process, and the corrosion resistance of the thin coating is low. Further, as the strength of materials increases to 2000MPa or more, the problem of hydrogen embrittlement has become a focus of attention. The process window for hot forming austenitization, which combines toughness and hydrogen embrittlement issues, is currently an urgent need for most customers.

Disclosure of Invention

The invention mainly aims to provide aluminized silicon steel, a hot forming component and a production process thereof, so as to solve the technical problem that the conventional aluminized silicon steel cannot be compatible with toughness and hydrogen embrittlement.

In order to achieve the above object, the present application provides an aluminized silicon steel comprising a steel substrate and a pre-plating layer disposed on the steel substrate;

The pre-plating layer comprises an intermediate layer and an aluminum silicon plating layer; the nominal thickness of the aluminum silicon coating is 10-33 mu m; the Al-Si coating contains 5-40% of Al-Si phase and 0.1-15% of Al-Si-Fe phase, and the dispersion index of the Al-Si phase and the Al-Si-Fe phase in the Al-Si coating is more than or equal to 0.05;

wherein the mass fraction of silicon in the Al-Si phase is 30-50%; the mass fraction of iron in the Al-Si-Fe phase is 10-35%, and the mass fraction of silicon is 3-15%;

preferably; the aluminum-silicon coating contains 10-30% of Al-Si phase and 0.1-10% of Al-Si-Fe phase, wherein the mass fraction of silicon in the Al-Si phase is 30-50%; the mass fraction of iron in the Al-Si-Fe phase is 10-35%, and the mass fraction of silicon is 3-15%.

According to an embodiment of the present application, the al—si phase includes an Al _nSi_m phase; wherein n: m= (1.0 to 3.0): 1, a step of; the proportion of the Al _nSi_m phase in the Al-Si phase is more than or equal to 50 percent.

According to an embodiment of the present application, the Al _nSi_m phase includes at least one of Al ₄Si₃ and Al ₄Si₂.

According to an embodiment of the present application, the Al-Si-Fe phase comprises a Fe _aSi_bAl_c phase; wherein a is b and c= (1-2) 1 (4-9); the proportion of the Fe _aSi_bAl_c phase in the Al-Si-Fe phase is more than or equal to 50 percent. The Fe _aSi_bAl_c phase includes fesai ₄ phase and Fe ₂SiAl₇ phase.

The application provides another aluminized silicon steel, which comprises a steel matrix and a pre-plating layer arranged on the steel matrix; the pre-plating layer comprises an intermediate layer and an aluminum silicon plating layer; the aluminum-silicon coating comprises aluminum flowers; the nominal thickness of the aluminum-silicon coating is 10-20 mu m, the aluminum flower meets the condition that coordinate points formed by the aluminum flower area (mm ²) and the aluminum flower convexity (mu m) are located in a first convex pentagon, and the first convex pentagon is surrounded by five points (2, 3), (150,3), (350,7), (350, 35), (2, 35).

According to an embodiment of the present application, the aluminum-silicon plating layer includes aluminum flowers; the nominal thickness of the aluminum-silicon coating is 19-33 mu m, the aluminum flower meets the condition that coordinate points formed by the aluminum flower area (mm ²) and the aluminum flower convexity (mu m) are located in a second convex pentagon, and the second convex pentagon is surrounded by five points (4, 5), (170,5), (400, 12), (400, 40), (4, 40).

According to an embodiment of the present application, the aluminum-silicon plating layer includes aluminum flowers; the nominal thickness of the aluminum-silicon coating is 10-20 mu m, the aluminum flower meets the condition that a coordinate point formed by the unit area aluminum lace boundary length (1/mm) and the aluminum flower convexity (mu m) is located in a third convex pentagon, and the third convex pentagon is surrounded by five points (0.1,7), (0.17,3), (10, 3), (10, 35) and (0.1, 35).

According to an embodiment of the present application, the aluminum-silicon plating layer includes aluminum flowers; the nominal thickness of the aluminum-silicon coating is 19-33 mu m, the aluminum flower meets the condition that a coordinate point formed by the unit area aluminum lace boundary length (1/mm) and the aluminum flower convexity (mu m) is located in a fourth convex pentagon, and the fourth convex pentagon is surrounded by five points (0.08, 12), (0.16,5), (8, 5), (8, 40) and (0.08, 40).

The application discloses a preparation method of aluminized silicon steel, which comprises the following steps:

Annealing the steel substrate to be plated, and then dip-plating in dip-plating liquid to obtain a dip-plated steel substrate; the dip coating liquid comprises the following components in percentage by mass: 8-11% of Si; fe:1 to 4 percent; the balance of Al and unavoidable impurities;

cooling the dip-plated steel matrix to 570-650 ℃ at a speed of 2-20 ℃/s, and maintaining the temperature of 570-650 ℃ for 1-20 seconds to obtain primary cold dip-plated steel;

Cooling the primary cold dip plated steel to 300 ℃ continuously at an average cooling rate of 5-25 ℃/s in a temperature regulating device under the condition of heating gas, and keeping the temperature for 2-30 seconds to obtain secondary cold dip plated steel; the temperature of the temperature regulating device is 300-570 ℃; the temperature of the heating gas is more than or equal to 100 ℃, and the total suspended particles of the gas is less than or equal to 0.2 mg/cubic meter;

and cooling the second cold dip plated steel to room temperature to obtain the precoated steel.

According to an embodiment of the present application, the immersion plated steel substrate is cooled to 570 ℃ at a rate of 2 to 15 ℃/s and maintained at 570 ℃ for 1 to 10 seconds to obtain the primary cold dip plated steel.

According to the embodiment of the application, the primary cold dip steel is cooled to 300 ℃ at an average cooling rate of 5-20 ℃/s, and the heat preservation time is 2-20 seconds, so that the secondary cold dip steel is obtained.

According to the embodiment of the application, the annealing temperature in the annealing step of the steel substrate to be plated is 700-850 ℃ and the annealing time is 1-20 minutes; the temperature of the annealed steel matrix to be plated entering the immersion plating solution is 600-700 ℃.

The application also discloses precoated steel, which is obtained by cold rolling and finishing of aluminized silicon steel; the precoated steel comprises a steel matrix and a finishing coating arranged on the steel matrix; the finishing coating is obtained by at least one of cold rolling and finishing;

The finishing coating comprises an intermediate layer and an aluminum-silicon coating; the nominal thickness of the aluminum silicon coating is 10-33 mu m; the Al-Si coating contains 5-40% of Al-Si phase and 0.1-15% of Al-Si-Fe phase, and the dispersion index of the Al-Si phase and the Al-Si-Fe phase in the Al-Si coating is more than or equal to 0.05;

Wherein the mass fraction of silicon in the Al-Si phase is 30-50%; the mass fraction of iron in the Al-Si-Fe phase is 10-35%, and the mass fraction of silicon is 3-15%.

The application also discloses a hot forming component, which comprises a steel matrix and a component coating; the component plating is generated by interdiffusion between the steel substrate and an aluminum silicon precoat;

The member plating layer comprises an inter-diffusion layer, a first intermediate layer, a first Al-rich intermetallic compound layer, a second intermediate layer and a second Al-rich intermetallic compound layer which are sequentially stacked; the inter-diffusion layer is positioned at the innermost side of the component plating layer;

The first Al-rich intermetallic compound layer is of a discontinuous structure, and the proportion of the first Al-rich intermetallic compound layer to the length of the layer is less than or equal to 80%; the second Al-rich intermetallic compound layer is of a quasi-continuous structure and occupies a continuous length proportion of the layer more than or equal to 20 percent;

Preferably, the first Al-rich intermetallic compound layer accounts for 1-50% of the length of the layer; the second Al-rich intermetallic compound layer accounts for more than or equal to 50% of the continuous length of the layer; more preferably; the second Al-rich intermetallic compound layer accounts for 50-90% of the continuous length of the layer.

According to an embodiment of the present application, the member plating layer further includes a surface layer located outside the second Al-rich intermetallic compound layer.

According to an embodiment of the present application, the grain sizes of the first intermediate layer, the second intermediate layer, and the surface layer are 30 μm or less; preferably; the first intermediate layer, the second intermediate layer, and the grain size are 25 μm or less; more preferably, the first intermediate layer, the second intermediate layer, and the grain size are 15 μm or less. The grain size of the intermediate layer of the coating of the application is the average grain size of the coating observed in cross section.

According to an embodiment of the present application, the total thickness of the member plating layer is 5 μm to 60 μm; preferably, the total thickness of the member plating layer is 20 μm to 55 μm; preferably, the total thickness of the member plating layer is 26 μm to 50 μm; further preferably, the total thickness of the member plating layer is 30 μm to 50 μm.

The application also discloses another hot forming component, which comprises a steel matrix and a component coating; the component plating is generated by interdiffusion between the steel substrate and an aluminum silicon precoat; the member plating layer has at least four Si concentration peaks in the thickness direction.

According to an embodiment of the present application, the at least four Si concentration peaks include a first Si concentration peak, a second Si concentration peak, a third Si concentration peak, and a fourth Si concentration peak from the component plating surface to the steel substrate;

the distance between the first Si concentration peak and the surface of the component plating layer is more than or equal to 0.25 mu m.

According to the embodiment of the application, the distance between the first Si concentration peak and the surface of the component plating layer is more than or equal to 0.45 mu m.

According to the embodiment of the application, the distance between the first Si concentration peak and the surface of the component plating layer is more than or equal to 0.75 mu m.

According to the embodiment of the application, the distance between the first Si concentration peak and the surface of the component plating layer is more than or equal to 1.5 mu m.

According to the embodiment of the application, the concentration value of the minimum peak value of the at least four Si concentration peaks after the back bottom is subtracted is more than or equal to 0.01%.

According to an embodiment of the application, the concentration value of the minimum peak is not less than 0.025%.

According to an embodiment of the application, the concentration value of the minimum peak is equal to or greater than 0.05%.

According to an embodiment of the application, the concentration value of the minimum peak is not less than 0.25%.

The invention also discloses a production process of the thermal forming component, which comprises the following steps:

heating the aluminized silicon steel or the precoated steel to an austenite region, wherein the heat preservation temperature is 880-950 ℃ and the heat preservation time is 3-15 minutes; the heating atmosphere is air, and the dew point is less than or equal to 0 ℃;

And cooling the heat-preserving steel plate, taking out the heated steel plate, adopting a die to press and deform the steel plate within 10 seconds, and cooling the steel plate to below 200 ℃.

The invention also discloses a motor vehicle comprising the thermoforming member.

In the aluminized silicon steel, the Al-Si phase and the Al-Si-Fe phase in the aluminized silicon coating are suitable in proportion, the dispersion index is suitable, the crystal grains of the thermoforming member which is conducive to subsequent production are smaller, and the double-layer Al-rich intermetallic compound layer is provided, so that the coating toughness and the environmental tolerance of the thermoforming member are improved, the crack sensitivity of the thermoforming member is reduced, and the thermoforming member also has the advantages of improving hydrogen embrittlement resistance, corrosion resistance and the like.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to the structures shown in these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a typical plated aluminum pattern of a strip of the present invention prior to thermoforming;

FIG. 2 is a typical plated aluminum flower morphology of a component of the invention after thermoforming;

FIG. 3 is a typical coating metallographic structure of a component of the invention after thermoforming;

FIG. 4 is a typical coating metallographic structure of a conventional thermoformed component after thermoforming;

FIG. 5 is a deformed plating structure of a component of the invention after thermoforming;

FIG. 6 is a deformed plating structure of a component of a conventional hot formed steel after hot forming;

FIG. 7 is a schematic illustration of the structure of the pre-plating layer prior to thermoforming;

FIG. 8 is a coating structure of a component of the present invention after thermoforming;

FIG. 9 is a plating structure of a conventional thermoformed component after thermoforming;

FIG. 10 shows the distribution of Si and Fe elements in the section of the aluminized silicon steel coating of the present invention;

FIG. 11 shows that the aluminum flower area of the surface of the strip steel of the present invention before thermoforming is 200mm ² or more;

FIG. 12 shows that the aluminum flower area of the surface of the strip steel of the present invention before thermoforming is 9mm ² or less;

FIG. 13 is a coating composition characteristic of a component of the present invention after thermoforming;

fig. 14 is a coating composition characteristic of a conventional member after thermoforming.

The achievement of the object, functional features and advantages of the present invention will be further described with reference to the drawings in connection with the embodiments.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, are intended to fall within the scope of the present invention.

It should be noted that all directional indicators (such as upper and lower … …) in the embodiments of the present invention are merely used to explain the relative positional relationship, movement conditions, etc. between the components in a specific posture (as shown in the drawings), and if the specific posture is changed, the directional indicator is changed accordingly.

Furthermore, descriptions such as those referred to as "first," "second," and the like, are provided for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implying an order of magnitude of the indicated technical features in the present disclosure. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature.

Moreover, the technical solutions of the embodiments of the present invention may be combined with each other, but it is necessary to be based on the fact that those skilled in the art can implement the embodiments, and when the technical solutions are contradictory or cannot be implemented, it should be considered that the combination of the technical solutions does not exist, and is not within the scope of protection claimed by the present invention.

The applicant has made a great deal of research on a thermoformed member, and the existing thermoformed member is mostly of a four-layer structure, which specifically includes: (a) an inter-diffusion layer; (b) an intermediate layer; (c) an Al-rich intermetallic layer; (d) a surface layer. And, the Al-rich intermetallic compound layer is a quasi-continuous structural layer. I.e. in the gold phase diagram the length of the Al-rich intermetallic layer is a large proportion, e.g. 90%, of the length of the structural layer. The overall visual golden phase diagram is substantially continuous. The length of the structural layer is the total length of the plating layer measurement.

The inventors have found that brittle Al-rich intermetallic compounds tend to be present at the interface of the interdiffusion layer and the first intermediate layer (i.e. the surface of the interdiffusion layer), and that when such Al-rich intermetallic compounds at the surface of the interdiffusion layer are thicker, cracks initiated at the surface of the coating layer will almost propagate towards the steel substrate during bending of the material. However, when the Al-rich intermetallic compound on the surface of the inter-diffusion layer is reduced, the difficulty of the crack propagation from outside into the inter-diffusion layer is increased, even the inter-diffusion layer is kept intact, and the phenomenon that the crack is initiated by the steel matrix is caused, which means that the reduction of the Al-rich intermetallic compound thickness on the surface of the inter-diffusion layer helps to improve the plasticity of the inter-diffusion layer, and further, the propagation of the crack from the surface into the steel matrix can be blocked. Further studies have found that the first Al-rich intermetallic compound layer tends to merge with the Al-rich intermetallic compound on the surface of the inter-diffusion layer to disappear, and this combination not only thickens the Al-rich intermetallic compound on the surface of the inter-diffusion layer, but also tends to cause the Al-rich intermetallic compound on the surface of the inter-diffusion layer to form sharp corners where stress concentration tends to occur, thereby facilitating initiation and propagation of cracks. If the crack continues to propagate and propagate from the inside, the crack can further promote the cracking of the steel matrix until reaching the interface between the steel matrix and the inter-diffusion layer.

After deformation (e.g., bending), if a large number of cracks appear in the interdiffusion layer, hydrogen can be facilitated to invade into the martensitic structure of the steel matrix, so that the complete interdiffusion layer can not only improve the bending toughness of the material, but also improve the hydrogen embrittlement resistance of the material to a certain extent.

Therefore, the first Al-rich intermetallic compound layer specially provided by the invention can share the enrichment degree of the Al-rich intermetallic compound in the inter-diffusion layer, thereby improving the plasticity of the inter-diffusion layer. Particularly when the thickness of the coating after thermoforming exceeds 26 μm, a sufficient amount of Al-rich intermetallic compounds can be formed in the coating. According to the invention, a part of the Al-rich intermetallic compound on the surface of the inter-diffusion layer is decomposed to form a new first Al-rich intermetallic compound layer, so that the plasticity of the inter-diffusion layer is improved, and the number of crack penetration is reduced.

In order to form the hot-formed member having the above structure, the raw material aluminum-plated silicon steel or the polished aluminum-plated silicon steel (hereinafter, precoated steel) must satisfy specific conditions. The aluminized silicon steel or the finished aluminized silicon steel (hereinafter, precoated steel) will be described below, respectively.

The pre-plating layer comprises an intermediate layer and an aluminum silicon plating layer. The nominal thickness of the aluminum silicon coating is 10-33 mu m. The Al-Si coating contains 5-40% of Al-Si phase and 0.1-15% of Al-Si-Fe phase, and the dispersion index of the Al-Si phase and the Al-Si-Fe phase in the Al-Si coating is more than or equal to 0.05. Wherein the mass fraction of silicon in the Al-Si phase is 30-50%. The mass fraction of iron in the Al-Si-Fe phase is 10-35%, and the mass fraction of silicon is 3-15%.

The distribution of Si and Fe elements in the section of the coating can be scanned by an energy spectrometer (EDS) (as shown in figure 10), and phases with dense distribution and bright positions of the Si and Fe elements in the coating are respectively Al-Si and Al-Si-Fe phases. Image software (e.g., image-pro Plus) was then used to calculate the ratio of Al-Si phase to Al-Si-Fe to the coating. When calculating the ratio, the interdiffusion layer between the plating layer and the substrate should be removed. In order to ensure that the detection result is representative, the detection can be generally carried out in a range of the section length of the continuous coating being more than or equal to 100 mm.

Aluminized silicon steel is typically formed by hot dip coating of a steel substrate. The steel matrix comprises a steel billet, hot rolled strip steel and cold rolled strip steel. The steel substrate to be plated is generally in the form of a flat steel strip, the dimensions of which are referred to in GB708-2006, also referred to in the industry as steel strip, strip steel or sheet. Such naming does not affect the explanation of the invention. The steel substrate to be plated is typically 0.5 to 3.5mm thick.

The steel substrate to be plated, namely steel for hot dip plating, comprises a hot rolled steel plate and a cold rolled steel plate or is commonly called strip steel. The steel substrate to be plated may be in the form of coil stock, sheet stock, parts, etc., and the steel substrate to be plated typically used for continuous annealing is in the form of coil stock. No matter what geometry the steel substrate to be plated is in, it does not affect the explanation of the invention. The hot dip plated steel strip is cut into steel plates with proper sizes, and the steel plates are hot formed to obtain parts, sheets and other components with required geometric sizes. No matter what geometry the thermoformed component is in, it does not affect the explanation of the invention. The coating layer can be an upper and lower double-sided coating layer or a certain surface coating layer.

In some embodiments, the steel substrate is a boron-containing intrusion resistant automotive thermoformed steel comprisingOr a range of ingredients: c:0.18 to 0.45 percent, mn:0.3 to 3.0 percent, B:0.0008 to 0.005% of an alloying element which can be added. The tensile strength of the material after thermoforming is more than or equal to 1500MPa, and the embodiment is especially aimed at the material with the tensile strength of more than or equal to 1800MPa after thermoforming.

In some embodiments, the steel is a hot formed steel for automobiles for niobium-containing impact energy absorption, comprisingOr a range of ingredients: c:0.03 to 0.12 percent, mn:0.15 to 2.5 percent, nb:0.02 to 0.10 percent of additively alloying elements including additively B:0.0008 to 0.005 percent. The tensile strength of the material after thermoforming is less than or equal to 1500MPa, and the embodiment is particularly aimed at the material with the tensile strength of 900-1500 MPa after thermoforming.

The aluminum silicon coating of the aluminum-plated silicon steel comprises (1) an intermediate layer; (2) aluminum silicon plating. The aluminum-silicon coating contains 5-40% of Al-Si phase, and the mass fraction of silicon in the Al-Si phase is 30-50%; the Al-Si coating contains 0.1-15% of Al-Si-Fe phase, 10-35% of iron in the Al-Si-Fe phase and 3-15% of silicon.

Through intensive researches of the inventor, the inventor finds that a certain proportion of Al-Si phase and Al-Si-Fe phase can be prepared in an aluminum-silicon coating of the pre-coated strip steel by reasonably controlling the manufacturing process (as shown in figure 9). The Al-Si phase and the Al-Si-Fe phase are key sources of the Al-rich intermetallic compound of the plating layer in the thermoforming process, and the distribution form and the quantity of the Al-Si phase and the Al-Si-Fe phase of the pre-plating layer determine the position and the quantity of the Al-rich intermetallic compound after thermoforming to a great extent. When the Al-Si phase and the Al-Si-Fe phase of the pre-plating layer are more and are distributed in a dispersing way, the generation of the first Al-rich intermetallic compound layer after thermoforming is facilitated. When the Al-Si phase and the Al-Si-Fe phase of the pre-plating layer are less and intensively distributed in the plating layer, the first Al-rich intermetallic compound layer after the hot forming is hardly present, and instead, a single layer of Al-rich intermetallic compound of the conventional hot formed steel is substituted, so that the double layer Al-rich intermetallic compound of the present invention cannot be obtained.

In order to obtain the double-layer Al-rich intermetallic compound structure after thermoforming, the Al-Si phase and the Al-Si-Fe phase should be distributed in a dispersed manner in the pre-plating layer, and not be gathered into a linear shape or a large block shape. The Al-Si coating contains 5-40% of Al-Si phase, and the mass fraction of silicon in the Al-Si phase is 20-50%; the Al-Si coating contains 0.1-15% of Al-Si-Fe phase, 10-35% of iron in the Al-Si-Fe phase and 3-15% of silicon. Preferably, the aluminum-silicon coating contains 10-30% of Al-Si phase, and the mass fraction of silicon in the Al-Si phase is 30-50%; the Al-Si coating contains 0.1-15% of Al-Si-Fe phase, 10-35% of iron in the Al-Si-Fe phase and 3-15% of silicon.

To better illustrate the features of the present invention, the degree of Al-Si phase and Al-Si-Fe dispersion of the present invention is explained using a dispersion index. In the range of 20X 100 square micrometers of the aluminum silicon coating (1), each of the Al-Si phase and the Al-Si-Fe phase which are uniform in size and are discontinuous remarkably are simplified into particles with geometric centers, or each of the Al-Si phase and the Al-Si-Fe phase with the area more than or equal to 1 square micrometer is simplified into particles, and adjacent 3 particles are connected. If the triangle formed by connecting 3 particles is not an obtuse triangle, the triangle is marked as a class A triangle. If the triangle is an obtuse triangle, the triangle is marked as a class B triangle. The dispersion index is defined as the ratio of class A triangles to the total number of triangles. The greater the index, the greater the degree of dispersion. In the present invention, when the dispersion index is not less than 0.05, the first Al-rich intermetallic compound layer tends to be formed at this position, that is, a 6-layer plating structure of an intermetallic compound containing double layers of Al (first Al-rich intermetallic compound layer and second layer) is easily formed after thermoforming. Preferably, the local dispersion index is not less than 0.1.

In the case where the above conditions are satisfied, the amount of ③ of the Al-Si phase and the Al-Si-Fe phase of the plating layer is small and the boundary is clear. Otherwise, the number of the ① phases of the Al-Si phase and the Al-Si-Fe phase of the plating layer is more, and the boundary is fuzzy; ② Fewer, boundary blurring.

The dispersion distribution of the present invention is particularly important in this location in order to avoid local Al-Si and Al-Si-Fe phase aggregation, resulting in too thick and sharp Al-rich intermetallic compounds at the surface of the inter-diffusion layer. The dispersion distribution can promote the formation of the first Al-rich intermetallic compound layer, and the phenomenon that the Al-rich intermetallic compound on the surface of the inter-diffusion layer is too thick and sharp is avoided. The discontinuous first Al-rich intermetallic compound layer obtained by the method can occupy more than 0.5 percent of the considered structural layer while meeting the requirements of the content proportion and the dispersion index of the Al-Si phase and the Al-Si-Fe phase. Preferably, the proportion of the first Al-rich intermetallic compound layer to the structural layer in question is more than 1%. The ratio is the ratio of the length obtained by connecting the first Al-rich intermetallic compound layer to the length of the structural layer, and the length of the structural layer is the total length measured by the plating layer.

The applicant has also found that a great deal of literature has been devoted to a detailed analysis of the coating structure of the pre-coating of existing hot-formed steel, which is believed to consist essentially of intermetallic compounds formed by eutectic reactions of pure Al and pure Si in the pre-coating of the steel strip prior to austenitization (prior to hot-forming heating). The coating consists of 3 parts, and the outermost layer is a pure Al layer which comprises a small amount of Si-rich phase and Fe-Al-Si ternary alloy; the middle layer is a Fe-Al-Si ternary alloy phase; the inner layer is an Fe-Al alloy layer, and the main components are Fe ₂Al₅ and FeAl ₃. The pure Si phase is in a long and thin strip shape, and the color is brighter. A brighter interlayer was present between the coating and the steel substrate, approximately 5mm thick, which was analyzed as the Fe ₂SiAl₇(τ₅ phase). A thin compound layer consisting of Fe ₂Al ₅ and FeAl ₃ is present between the intermetallic compound Fe ₂SiAl₇ and the steel substrate.

The Al-Si phase exists mainly in the cluster structure of Al _nSi_m or contains not more than 1% of Fe, and the atomic structure stability of the Al-Si phase has higher correlation with the bonding mode and bonding energy.

In some embodiments, the Al-Si phase comprises an Al _nSi_m phase. Wherein n: m= (1.0 to 3.0): 1. the proportion of the Al _nSi_m phase in the Al-Si phase is more than or equal to 50 percent. Specifically, the Al _nSi_m phase includes at least one of Al ₄Si₃ and Al ₄Si₂.

The invention is mainly aimed at the atomic ratio n: the Al-Si phase with m ranging from 1.0 to 3.0 is controlled to obtain a certain proportion of the required Al-Si phase, and the phase contributes to the formation of the coating structure after thermoforming. Further, the critical precipitated phases include phases having an Al-Si atomic ratio of between 1.3 and 2.5, such as Al ₄Si₃、Al₄Si₂. Such Al-Si phases (including Al ₄Si₃、Al₄Si₂) are required as the precipitate phases for the desired control of the present invention. Because the bonding property of the phase is determined, al ₄Si₃、Al₄Si₂ cannot be stabilized, and the method adopts the means of heat preservation cover, coating heating, high-purity dry air and the like in the coating control cooling process, so that the stability of Al ₄Si₃、Al₄Si₂ can be improved, and more granular and more effective Al-Si phases can be obtained.

In some embodiments, the Al-Si-Fe phase comprises an Fe _aSi_bAl_c phase; wherein a is b and c= (1-2) 1 (4-9); the proportion of the Fe _aSi_bAl_c phase in the Al-Si-Fe phase is more than or equal to 50 percent. The Fe _aSi_bAl_c phase includes fesai ₄ phase and Fe ₂SiAl₇ phase.

The Al-Si-Fe phase is the main existence form of Fe in the coating, and is the product of the Fe element of the steel matrix which is diffused into the plating solution and then recombined with the Al-Si phase to form the Al-Si-Fe phase. The prior researches show that solid acicular FeSiAl ₄(τ₆ phase is generated in the plating layer in the cooling process of the hot dip plating solution. However, the inventors found that in practice Fe ₂SiAl₇(τ₅ phase is also present in the coating). The Al-Si-Fe phase (mainly comprising tau ₅、τ₆ phase) is the required precipitated phase for the present invention.

In some embodiments, the aluminum silicon plating includes aluminum flowers. The nominal thickness of the aluminum-silicon coating is 10-20 mu m, the aluminum flower meets the condition that coordinate points formed by the aluminum flower area (mm ²) and the aluminum flower convexity (mu m) are located in a first pentagon, and the first pentagon is surrounded by five points (2, 3), (150,3), (350,7), (350, 35) and (2, 35).

The aluminum-silicon plated steel plate forms a single aluminum solidification layer at about 600 ℃, and the aluminum-silicon solidified phase structure forms a flower-shaped polygon pattern in the solidification process, and the flower-shaped polygon pattern is called as aluminum flower.

The thickness of the coating and the area of the aluminum flower have a certain relation, and the larger the thickness of the coating is, the more easily the aluminum flower grows. This is mainly related to the low cooling rate of the thick coating. When the thickness of the coating is more than or equal to 10 mu m, the area of the aluminum flower can be controlled. When the thickness of the coating is more than or equal to 19 mu m, the area of the aluminum flower is more suitable. The average thickness of the preplating layer is 10 μm to 33 μm. Preferably, the average thickness of the pre-plating layer is 19 μm to 33 μm.

The inventors found that the continuity of the first Al-rich intermetallic compound layer has a certain relationship with the size of the aluminum flower. The larger aluminum flower area can also retain more complete aluminum dendrites, and reduce the number of aluminum grain boundaries. The grain boundaries often have a large number of precipitates, which become sites where diffusible hydrogen can accumulate, and once the conditions are met, the diffusible hydrogen is transferred into the steel matrix. The defects in the complete crystal grains are fewer, diffusible hydrogen is reduced, and invasion of hydrogen into the steel matrix can be blocked to a certain extent. The resistance to hydrogen embrittlement of the thermoformed part is related to the coarse aluminium flower. Therefore, the aluminum flower area is increased to 4mm ² and above, the thickness of the preplating layer is kept to be more than 10 mu m, the diffusible hydrogen content of the plating layer is reduced, and the diffusion degree of hot hydrogen to the steel matrix is relieved. The average aluminum flower area is more than or equal to 16mm ², and the thickness of the preplating layer is kept to be more than 19 mu m, so that the number of crystal boundaries is obviously reduced, and the diffusion quantity of hydrogen along the crystal boundaries of the aluminum flower to the inside is reduced. In addition, when the aluminum flower area is 2mm ² and below, and the plating layer thickness is less than 10 mu m, the protection effect of the aluminum flower is affected, because the thickness of the aluminum flower boundary is thinner, the invasion distance of hydrogen at the position is greatly reduced, the invasion of hydrogen into the steel matrix is easier, and small aluminum flowers and thin plating layers are not beneficial to blocking hydrogen intake.

In the related art, since the above-described protective effect of the aluminum flower is not found, it is considered that the aluminum flower affects the beauty of the final thermoformed article, and it is generally desirable that the aluminum flower area is as small as possible, and no aluminum flower is provided. For example, the aluminum flower is smaller or no aluminum flower is generated by controlling the coating process. Or the aluminum flower is covered by spraying powder.

In the application, the nominal thickness is the set thickness of the aluminum silicon coating, namely the target thickness of the aluminum silicon coating. For convenience of comparative analysis and explanation, the aluminum flower convexity of the application is the convexity of the strip steel aluminum flower after production when the surface of the strip steel is not plated (such as finishing).

The invention needs to provide larger aluminum flowers for the plating layer, and the larger aluminum flowers can cause the increase of the thickness difference of the local part of the plating layer. The growing process of the aluminum flower is the nucleation and growth process of the aluminum flower, the center of the aluminum flower is first nucleated and grown, the growing process is continuously solidified and thickened, and the thickness is larger. The aluminum flower edges solidify and grow at the central nucleation point where the thickness is thinner. When the aluminum flower area is above 4mm ², the uneven thickness affects the distribution of Al-Si phase and Al-Si-Fe phase of the plating layer. When the aluminum flower area is more than 16mm ², the degree of uneven thickness is more obvious. After the aluminum flower is enlarged by adopting the coating cooling process, obvious thickness difference can be seen under a microscope, and even the coating has uneven feeling when being touched by hands.

The greater thickness of the coating at the center of the flowers than at the boundaries of the flowers is one of the key factors in promoting the 6-layer structure after thermoforming of the invention, and the presence of this difference is beneficial in promoting the formation of sufficient amounts of Al-Si phase and Al-Si-Fe phase near the center of the flowers within the pre-coat. The convexity (C) of the aluminum flower is defined as: on the pre-plating strip steel, the difference of the average value of three points of the maximum plating thickness near the center of the aluminum plating flower minus the average value of three points of the minimum thickness near the edge of the aluminum lace. The convexity of the aluminum flower is generally more than or equal to 1 mu m. In order to meet the quality requirement of the invention, the convexity of the aluminum flower is at least more than or equal to 3 mu m, and especially when the convexity of the aluminum flower of the coating is more than or equal to 5 mu m, the effect of promoting the 6-layer structure after thermoforming is more obvious. For materials with larger thickness and single-sided coating thickness of 19-33 mu m, the convexity of the aluminum flower is at least more than or equal to 5 mu m.

Because the Al-Si phase and the Al-Si-Fe phase in the plating layer are basically formed before the plating layer is polished and straightened, even if the plating layer is polished, the convexity of the aluminum flower is less than 3 mu m, and the requirements of the invention can be met. Therefore, the convexity requirement of the aluminum flower plating layer required by the invention is the convexity requirement of the aluminum flower plating layer before surface treatment (such as finishing, rolling and thermoforming). In general, when the thickness of the preplating layer is set to 10 to 20 μm (nominal thickness 10 to 20 μm), the maximum aluminum flower convexity may be not less than 35 μm because of the presence of the aluminum flower convexity of 5 to 40 μm. When the layer thickness is set to 19-33 mu m (the nominal thickness is 19-33 mu m), the thickness range distribution of the preplating layer can be 10-50 mu m, so that the maximum aluminum flower convexity can be more than or equal to 40 mu m. Without the process of the present invention, it is difficult to obtain the convexity required for the present invention.

Analysis shows that the convexity of the aluminum flower is related to the thickness of the plating layer and the size of the aluminum flower. In general, the thinner the coating, the smaller the crown of the aluminum flower and the smaller the area of the aluminum flower, the smaller the crown of the aluminum flower. In order for the material properties after thermoforming to meet the requirements of the present invention, the relationship between the convexity of the aluminum flower, the area of the aluminum flower and the thickness of the plating should meet the following requirements.

C≥a·S

In the above formula: c is convexity of aluminum flower, and the unit is mu m; s is the area of aluminum flower, and the unit is mm ²; a is a coefficient, the unit is mu m/mm ², and the value of a is 0.02 for the convenience of calculation and description.

Preferably, (1) when the average thickness of the single-sided plating layer is < 19 μm, the coefficient is 0.02, that is: c is more than or equal to 0.02S. However, in order to meet the distribution requirement of the precipitated phase of the plating, the convexity of the aluminum flower is at least 3 μm when the thickness of the single-sided plating is less than 19 μm. (2) When the average thickness of the single-sided coating is more than or equal to 19 mu m, the coefficient is 0.03, namely: c is more than or equal to 0.03S. In order to meet the distribution requirement of the precipitated phase of the plating layer, when the thickness of the single-sided plating layer is more than or equal to 19 mu m, the convexity of the aluminum flower is at least 5 mu m.

Under ideal conditions, the growth of a single aluminum flower in a three-dimensional space can be equiaxed, namely the thickness of the aluminum flower is equal to the diameter of the aluminum flower, but the aluminum flower on the surface of the strip steel is larger, the thickness growth is limited, and the aluminum flower cannot be equiaxed but is flat. The convexity of the aluminum flower of the invention needs to be controlled to be limited, otherwise, the surface of the plating layer is too uneven. In general, the convexity of the aluminum flower should be less than or equal to 0.8 times the average thickness of the single-sided plating. Preferably, the convexity of the aluminum flower is less than or equal to 0.7 times of the average thickness of the single-sided plating layer. For ease of calculation and illustration, the maximum convexity of the aluminum flower should not exceed 40 μm.

Five points (2, 3), (150,3), (350,7), (350, 35), (2, 35) constituting the first pentagon, each point being a coordinate point formed by an aluminum flower area (mm ²) and an aluminum flower convexity (μm). Taking coordinate points (2, 3) as an example, the aluminum flower area (mm ²) of the point is 2, and the convexity (μm) of the aluminum flower is 3.

The nominal thickness of the aluminum-silicon coating is 10-20 mu m, and the corresponding aluminum flower meets the condition that a coordinate point formed by the aluminum flower area (mm ²) and the aluminum flower convexity (mu m) is located in the first pentagon. Under the condition, the continuity of the first Al-rich intermetallic compound layer of the thermal forming part is reduced, and the structure of the double Al-rich intermetallic compound layers is easier to generate, so that the coating toughness and environmental tolerance of the thermal forming member are improved, the crack sensitivity of the thermal forming member is reduced, and the thermal forming member also has the advantages of improving hydrogen embrittlement resistance, corrosion resistance and the like.

In other embodiments. The nominal thickness of the aluminum-silicon coating is 19-33 mu m, the aluminum flower meets the condition that coordinate points formed by the aluminum flower area (mm ²) and the aluminum flower convexity (mu m) are located in a second pentagon, and the second pentagon is surrounded by five points (4, 5), (170,5), (400, 12), (400, 40), (4, 40).

The definition of the five points constituting the second pentagon is the same as the definition of the five points constituting the first pentagon, and will not be described again. The nominal thickness of the aluminum-silicon coating is 19-33 mu m, and the corresponding aluminum flower meets the condition that a coordinate point formed by the aluminum flower area (mm ²) and the aluminum flower convexity (mu m) is located in the second pentagon. Under the condition, the continuity of the first Al-rich intermetallic compound layer of the thermal forming part is reduced, and the structure of the double Al-rich intermetallic compound layers is easier to generate, so that the coating toughness and environmental tolerance of the thermal forming member are improved, the crack sensitivity of the thermal forming member is reduced, and the thermal forming member also has the advantages of improving hydrogen embrittlement resistance, corrosion resistance and the like.

In some embodiments, the aluminum silicon plating includes aluminum flowers. The nominal thickness of the aluminum-silicon coating is 10-20 mu m, the aluminum flower meets the condition that a coordinate point formed by the unit area aluminum lace boundary length (1/mm) and the aluminum flower convexity (mu m) is located in a third pentagon, and the third pentagon is surrounded by five points (0.1,7), (0.17,3), (10, 3), (10, 35) and (0.1, 35).

Because hydrogen intrusion is easier at aluminum grain boundaries, it is more stringent to control the cumulative length of grain boundaries per unit area rather than the area of aluminum, and not the length and width parameters of aluminum that are simple in the conventional art. However, by means of the invention, approximately equiaxed aluminum flowers can be obtained. The side lengths of all directional sides of the equiaxed aluminum flowers are approximately equal, namely the aluminum flowers are identical in all directions, and the overall outline is approximately round. That is, the circumference of the equiaxed aluminum flower is smaller than that of the anisometric aluminum flower (such as the aluminum flower with the approximate rectangle overall outline) under the condition of the same area.

Therefore, compared with the traditional aluminum plating technology, the cumulative boundary length of the aluminum flowers is greatly reduced, and even if the area of the aluminum flowers is smaller, the total boundary length of the aluminum flowers is smaller than that of an uncontrolled aluminum plating plate produced by the traditional technology. Therefore, the convexity (μm) of aluminum flower and the length (mm) of aluminum lace boundary are key technologies for determining the performance of the material of the invention. Because the length of the aluminum lace boundary is not easy to measure, the aluminum flower shape of the invention is basically similar to an equiaxial shape, and the stability of the aluminum flower shape is high, therefore, the relationship between the aluminum flower area and the aluminum flower convexity can be adopted to replace the requirements of the aluminum flower convexity and the aluminum lace boundary length.

Through research, this alternative scheme is effective within the present invention. For the traditional production process, even though the average area of the aluminum flower is within the required range of the invention, the cumulative length of the aluminum lace boundary in unit area exceeds the requirement of the invention because the shape of the aluminum flower is not controlled. The invention also provides the relation requirement of the convexity of the aluminum flower and the length of the aluminum lace boundary in unit area.

Therefore, in this example, (1) the nominal thickness of the single-sided plating layer is 10 to 20. Mu.m, the aluminum lace border length per unit area (1/mm) and the aluminum flower convexity (μm) should be within a pentagon surrounded by five points (0.1,7), (0.17,3), (10, 3), (10, 35), (0.1, 35).

In some embodiments, the nominal thickness of the aluminum-silicon coating is 19-33 μm, and the aluminum flower meets the condition that a coordinate point formed by the aluminum lace boundary length (1/mm) and the aluminum flower convexity (μm) in a unit area is located in a fourth pentagon, wherein the fourth pentagon is surrounded by five points (0.08, 12), (0.16,5), (8, 5), (8, 40) and (0.08, 40).

(2) The length (1/mm) of the aluminum lace boundary per unit area and the convexity (μm) of the aluminum flower should be within pentagons surrounded by five points (0.08, 12), (0.16,5), (8, 5), (8, 40), (0.08, 40).

The convexity of the plated aluminum flower in the actual delivery state can be influenced by finishing and tension leveling, and the convexity can be reduced. However, this does not have a serious adverse effect on the distribution of Al-Si and Al-Si-Fe in the coating.

Because the aluminum flower prepared by the embodiment of the application is approximately equiaxed. Compared with the prior art, the aluminum pattern area defined by the application, namely the average aluminum pattern area of the surface of the plating layer, is more beneficial to the technical requirements of the application. Thus, in some embodiments, the aluminum flower area is measured as follows:

(1) Taking a 300mm multiplied by 300mm sample at the 1/4 position of the width of the strip steel plate;

(2) Drawing 3 straight lines with the length of 100mm respectively on the upper surface and the lower surface of the sample plate along the transverse direction and the longitudinal direction, wherein the interval between the straight lines is more than 50mm;

(3) Counting the number of aluminum flowers on each line respectively, taking an average number a of the number of the horizontal aluminum flowers, and taking an average number b of the number of the vertical aluminum flowers;

(4) The aluminum flower area S, s=100×100/(a×b) was calculated.

Note that: the above sampling positions are merely representative, and if the strip steel size does not meet the requirement, the sampling positions and the line drawing positions can be adjusted, but the evaluation area is generally not less than 90000mm ².

S100: and (3) after annealing the steel substrate to be plated, dip-plating in dip-plating liquid to obtain the dip-plated steel substrate. The dip coating liquid comprises the following components in percentage by mass: 8-11% of Si. Fe:1 to 4 percent. The balance of Al and unavoidable impurities.

The steel matrix to be plated (namely strip steel) for hot dip plating comprises hot rolled strip steel and cold rolled strip steel, and the thickness is 0.5-3.5 mm.

The immersion plating solutions are typically placed in an aluminum pan. The composition of the immersion plating solution may also be expressed in terms of the composition of the aluminum pan. Namely, the components of the aluminum pot: 8-11% of Si; fe:1 to 4 percent; the balance of Al and unavoidable impurities.

And (3) entering the aluminum pot after the steel plating substrate is annealed, wherein the temperature of entering the aluminum pot is the entering temperature. In some embodiments, the annealed steel substrate to be plated is brought to a temperature of 600 to 700 ℃ in the immersion plating solution. Namely the temperature of the strip steel entering the pot is 600-700 ℃.

S200: cooling the dip plated steel matrix to 570-650 ℃ at a speed of 2-20 ℃/s, and maintaining the temperature of 570-650 ℃ for 1-20 seconds to obtain the primary cold dip plated steel.

In order to achieve the above requirements of Al-Si phase and Al-Si-Fe phase and uniformity of the coating, the invention adopts a method of cooling the coating under control and applying deformation to the coating. Namely the first stage cooling of step S200 and the second stage cooling of step S300.

In order to meet the requirements of the Al-Si phase and the Al-Si-Fe phase, air is used for cooling the strip steel after hot dip plating, and the average cooling rate of the strip steel is controlled to be less than or equal to 50 ℃/s within the range from the aluminum outlet pot to 300 ℃. Preferably, the average rate is 2 to 25 ℃/s. Preferably, the average speed of cooling the coating to 570 ℃ after the coating is discharged from the aluminum pot (cooling in the first stage) is 2-20 ℃/s. The average speed of the coating layer is 5-25 ℃ per second when the coating layer is cooled from 570 ℃ to 300 ℃ (second stage cooling). The controlled cooling contributes to the precipitation of the above-mentioned portions of the Al-Si phase and Al-Si-Fe phase.

In the first stage of cooling, the temperature is generally kept within the range of 570-650 ℃ and the temperature is kept for 1-20 seconds. The insulation can also be replaced by an insulation board, and when the insulation board is adopted, the insulation board is arranged on the two sides of the upper surface and the lower surface of the coating. The heat preservation measures are helpful for prolonging the time of the coating of the strip steel to stay in a high temperature area and maintaining the surface tension of the aluminum flower, thereby improving the convexity of the aluminum flower after the coating is solidified.

S300: and (3) cooling the primary cold dip plated steel to 300 ℃ continuously at an average cooling rate of 5-25 ℃/s in a temperature regulating device under the condition of heating gas, and keeping the temperature for 2-30 seconds to obtain the secondary cold dip plated steel. The temperature of the temperature regulating device is 300-570 ℃. The temperature of the heated gas is more than or equal to 100 ℃, and the total suspended particles of the gas is less than or equal to 0.2 mg/cubic meter.

In order to obtain the convexity and area of the aluminum flower required by the invention, the excessive cooling speed should be avoided, and the cooling speed of the second section less than or equal to 15 ℃/s is obtained. The cooling section can be provided with a temperature adjusting device, the heat preservation temperature is 300-570 ℃, and the heat preservation time is 2-30 seconds. Preferably, the temperature is 300-570 ℃, and the time is 5-20 seconds.

The measures such as cooling and heat preservation can not meet the requirement of aluminum flower growth. In order to meet the requirements of the aluminum flower area and convexity, the cooling section is provided with a gas heating device, the gas temperature during heating is more than or equal to 300 ℃, the temperature interval during heating the strip steel is 300-650 ℃, and the heating rate of the strip steel is controlled to be 0-25 ℃/s. The Total Suspended Particles (TSP) of the gas is less than or equal to 0.2 mg/cubic meter. The purpose of controlling the upper TSP limit is to reduce entrained particulates in the gas that may become aluminum flower shaped points, thereby increasing the aluminum flower so as to increase the aluminum lace border length per unit area.

The inventors deeply analyze the influence of the phase change heat release of the material on aluminum flower, and when the material releases heat in the cooling process, the effect of maintaining the temperature of the strip steel is achieved, the growth of aluminum flower is facilitated, and the Al-Si and Al-Si-Fe phases are particularly facilitated to meet the dispersion index of the invention. The energy applied by the above-mentioned insulation can be suitably reduced, i.e. the temperature of the heating gas of the cooling section can be suitably reduced. In general, the composition satisfies C:0.18 to 0.45 percent, mn:0.3 to 3.0 percent, B: when the temperature of the annealing is 0.0008-0.005%, and the heat preservation temperature is more than or equal to 730, the heat preservation time is more than or equal to 1 minute, then the phase change heat release effect exists in the cooling process after plating, and the gas temperature during heating implemented in the cooling section can be properly reduced, for example, the upper limit of the gas temperature is controlled, namely, the temperature is less than or equal to 650 ℃. Further, C:0.28 to 0.45 percent, mn:0.3 to 3.0 percent, B:0.0008 to 0.005 percent, when the heat preservation temperature of annealing is more than or equal to 730, the heat preservation time is more than or equal to 1 minute, and the gas temperature is 640 ℃ when heating is implemented in the cooling section.

When a certain amount of Cr, ni, V, mo strip steel is added into the strip steel, the exothermic temperature range has a descending trend, and the auxiliary heat of the heating gas is advanced so as to prevent the phase change exothermic time from being delayed to influence the growth of aluminum flowers. Specifically, when the steel strip meets the condition C:0.18 to 0.45 percent, mn:0.3 to 3.0 percent, B:0.0008 to 0.005 percent, cr:0.1 to 0.5 percent, when the heat preservation temperature of annealing is more than or equal to 730, the heat preservation time is more than or equal to 1 minute, and the temperature of the strip steel gas in the cooling stage is more than or equal to 305 ℃. Further, when the strip steel satisfies C:0.18 to 0.45 percent, mn:0.3 to 3.0 percent, B:0.0008 to 0.005 percent, cr:0.1 to 0.5 percent; ni+v+mo:0.1 to 1.5 percent, when the heat preservation temperature of annealing is more than or equal to 730, the heat preservation time is more than or equal to 1 minute, and the temperature of the strip steel gas in the cooling stage is more than or equal to 310 ℃. Further, when the strip steel satisfies C:0.28 to 0.45 percent, mn:0.3 to 3.0 percent, B:0.0008 to 0.005 percent, cr:0.1 to 0.5 percent; ni+v+mo:0.1 to 1.5 percent, and when two of three elements of Ni, V and Mo simultaneously meet the requirement of more than or equal to 0.1 percent, the heat preservation temperature of annealing is more than or equal to 730 percent, the heat preservation time is more than or equal to 1 minute, and the temperature of strip steel gas in the cooling stage is more than or equal to 315 ℃.

S400: and cooling the second cold dip plated steel to room temperature to obtain the precoated steel.

In this step, the strip may be cooled from 300 ℃ to room temperature using air and/or water.

In some embodiments, the immersion plated steel substrate is cooled to 570 ℃ at a rate of 2 to 15 ℃/s and maintained at 570 ℃ for 1 to 10 seconds to obtain the primary cold dip steel.

In some embodiments, the primary cold dip plated steel is cooled to 300 ℃ at an average cooling rate of 5-20 ℃/s for 2-20 seconds to obtain a secondary cold dip plated steel.

In some embodiments, the annealing temperature in the annealing step of the steel substrate to be plated is 700-850 ℃ and the annealing time is 1-20 minutes.

Annealing is carried out on the cold-rolled strip steel, the annealing temperature is 700-880 ℃, and the annealing time is 1-20 minutes. Preferably, the annealing temperature is 700-850 ℃ and the annealing time is 3-15 minutes. For hot rolled strip that is not cold rolled, the annealing temperature of the strip may be less than 700 ℃.

In some embodiments, a purge (e.g., using a nozzle blowing system, i.e., an air knife) is further included between step S100 and step S200 to remove excess plating solution from the surface, resulting in a strip having an average thickness (single-sided) of 10 μm to 33 μm. Preferably, the average thickness of the coating layer of the pre-coated strip steel is 19-33 μm.

In some embodiments, after the superfluous plating solution on the surface is removed by purging, at least an alternating magnetic field with the frequency of more than or equal to 1Hz is applied to the plating layer in a liquid state.

The invention needs to control the grain distribution direction of Al-Si-Fe phase in the coating, and after the strip steel is discharged from the air knife, at least an alternating magnetic field can be applied to the coating which is still in liquid state, the distribution of the Al-Si-Fe phase is controlled, and the frequency of the alternating magnetic field is more than or equal to 1Hz. The alternating magnetic field has stirring effect on the coating, so that excessive unfavorable cast coating grains can be prevented from being formed, and the stirring is beneficial to changing the distribution states of the Al-Si phase and the Al-Si-Fe phase and improving the dispersion index. The frequency of the alternating magnetic field is properly increased, for example, the frequency is more than or equal to 50Hz, and the electromagnetic stirring effect on the coating is more remarkable.

The application also discloses precoated steel, which is obtained by cold rolling and finishing of aluminized silicon steel. The precoated steel includes a steel substrate and a finishing coating disposed on the steel substrate. The finishing coating is obtained by at least one of cold rolling and finishing.

The finishing coating comprises an intermediate layer and an aluminum-silicon coating. The nominal thickness of the aluminum silicon coating is 10-33 mu m. The Al-Si coating contains 5-40% of Al-Si phase and 0.1-15% of Al-Si-Fe phase, and the dispersion index of the Al-Si phase and the Al-Si-Fe phase in the Al-Si coating is more than or equal to 0.05.

Wherein the mass fraction of silicon in the Al-Si phase is 30-50%. The mass fraction of iron in the Al-Si-Fe phase is 10-35%, and the mass fraction of silicon is 3-15%.

The precoated steel is obtained by cold rolling and finishing aluminized silicon steel. The precoated steel also has aluminum flowers. The convexity of the aluminum flower of the precoated steel can be influenced by finishing and tension leveling, and the convexity can be reduced. However, this does not have a serious adverse effect on the distribution of Al-Si and Al-Si-Fe in the coating, which is substantially the same as in aluminized silicon steel. Therefore, the proportion, the composition and the aluminum flower area of the Al-Si phase and the Al-Si-Fe phase of the precoated steel can be referred to the aluminized silicon steel, and are not repeated.

The application also discloses a hot forming component, which comprises a steel matrix and a component coating. The component coating results from interdiffusion between the steel substrate and the aluminum silicon precoat.

The member plating layer includes an inter-diffusion layer, a first intermediate layer, a first Al-rich intermetallic compound layer, a second intermediate layer, and a second Al-rich intermetallic compound layer, which are sequentially stacked. The interdiffusion layer is located at the innermost side of the member plating layer.

The first Al-rich intermetallic compound layer is of a discontinuous structure and occupies less than or equal to 80 percent of the length of the layer. The second Al-rich intermetallic compound layer is of a quasi-continuous structure and occupies a continuous length proportion of more than or equal to 20 percent.

To more clearly describe the structure of the thermoformed component, a more structurally complete thermoformed component is illustrated, including a coating having 6 structural layers. It should be noted that the surface layer does not have to be structured.

The thermoformed component coating comprises (a) an interdiffusion layer; (b) a first intermediate layer; (c) a first Al-rich intermetallic compound layer; (d) a second intermediate layer; (e) a second Al-rich intermetallic layer; (f) a surface layer.

Wherein:

(a) Interdiffusion layer: the thickness is 5-18 mu m, the hardness of the layer is HV50g and is 230-420. The layer comprises the following components in percentage by weight: 80-95% of Fe, 4-10% of Al and 0-5% of Si. At the interface between the inter-diffusion layer and the first intermediate layer, there is an intermetallic compound of the same composition as the first Al-rich intermetallic compound layer.

(B) A first intermediate layer: the thickness is 0-25 mu m, and the hardness of the layer is HV50g and 800-1000. The layer comprises the following components in percentage by weight: 35-47% of Fe, 50-61% of Al and 0-2% of Si.

(C) A first Al-rich intermetallic compound layer: the thickness is 0-15 mu m, the hardness of the layer is HV50g and is 450-650. The layer comprises the following components in percentage by weight: 50-70% of Fe, 30-35% of Al and 2-6% of Si. The first Al-rich intermetallic compound layer is of a discontinuous structure and occupies less than or equal to 80 percent of the continuous length of the layer. Preferably, the first Al-rich intermetallic compound layer has a discontinuous structure and occupies a continuous length of 1 to 50% of the layer. In the layer, the intermetallic compound rich in Al is required to have uneven plating thickness, and the formation difficulty of a thinner area (the plating thickness is less than or equal to 26 mu m) of the plating is more difficult, and the continuity is poorer. The continuity of the first Al-rich intermetallic compound layer is affected by the heating state, and the heating process should be kept continuously heated instead of setting different heating temperatures stepwise. In particular, a set temperature exceeding 940 ℃ should be avoided, while at the same time the actual temperature of the component should be avoided to exceed 950 ℃, otherwise when the holding time is sufficiently long, the first Al-rich intermetallic layer formed at high temperature will be completely incorporated by the interdiffusion layer, so that this layer completely disappears.

The inventors found that when the average area of the aluminum flower of the pre-plating layer is not less than 16mm ², more first Al-rich intermetallic compound layers are easily obtained. Especially when the average area of aluminum flowers is more than or equal to 64mm ², and the plating thickness of the pre-plating strip steel is more than 10 mu m, the continuity of the first intermetallic compound layer rich in Al is stronger, and the ratio of the intermetallic compound rich in Al to the continuous length of the layer is 1-30%. When the average area of aluminum flowers is more than or equal to 64mm ² and the plating thickness of the pre-plating strip steel is more than 19 mu m, the continuity of the first Al-rich intermetallic compound layer is stronger, and the Al-rich intermetallic compound accounts for 1-50% of the continuous length of the layer. And when the maximum area of the aluminum flower is more than or equal to 100mm ², a more typical excellent coating 6-layer structure after thermoforming is easy to obtain. The continuity of the first Al-rich intermetallic compound layer is related to the coating variation after thermoforming, such as when the thickness of the coating after thermoforming is less than 26 μm, the first Al-rich intermetallic compound layer almost merges with the interdiffusion layer due to the closer distance between the first Al-rich intermetallic compound layer and the Al-rich intermetallic compound on the surface of the interdiffusion layer. In addition, the excessive thickness of the inter-diffusion layer may affect the formation of the first Al-rich intermetallic compound layer, such as when the inter-diffusion layer thickness is 16 μm or more, the first Al-rich intermetallic compound layer is almost disappeared. The effect of the aluminum flower on the formation of the first Al-rich intermetallic compound layer is mainly influenced by the distribution of the Al-Si phase and the Al-Si-Fe phase in the preplating layer, when the aluminum flower is increased, more Al-Si phase and Al-Si-Fe phase are more easily formed near the center of the aluminum flower, and when the area of the aluminum flower is reduced, the aggregation effect is reduced, and the structural effect of the double-layer Al-rich intermetallic compound is reduced. The nucleation amounts of the Al-Si phase and the Al-Si-Fe phase required by the invention are controlled in an aluminum pot before plating. Then, through the subsequent process of the invention, the distribution of the Al-Si phase and the Al-Si-Fe phase gradually meets the requirements of the invention.

After thermoforming, the present invention should avoid excessive traditional 4-layer structures of the thermoformed steel, or fewer structural layers. Because Al-rich intermetallic compounds on the surface of the interdiffusion layer will be thickened when the number of structural layers is too small. But cannot meet the requirements of the invention, further resulting in the reduction of the plasticity, toughness and hydrogen embrittlement resistance of the material. However, even if the present invention inevitably has less than 6 layer structures in the locally existing portion of the plating layer, i.e., the first Al-rich intermetallic compound layer partially disappears, by implementing the technique of the present invention, the plasticity, toughness and hydrogen embrittlement resistance of the interdiffusion layer of the material are improved, for reasons related to the aluminum flower, al-Si phase, al-Si-Fe phase division characteristics of the plating layer, and the like. More critical is that the grains in the coating are refined.

(D) A second intermediate layer: the second intermediate layer has the same composition as the first intermediate layer. The first intermediate layer and the second intermediate layer will fuse together at the location where the continuity of the first Al-rich intermetallic compound layer is low, and such fusion tends to occur more easily as the aluminum flower area is smaller and the plating layer is thinner.

(E) A second Al-rich intermetallic compound layer: the second Al-rich intermetallic compound layer and the first Al-rich intermetallic compound layer have the same composition, are of a quasi-continuous structure and generally occupy the continuous length proportion of the layer more than or equal to 20 percent.

In some embodiments, the continuity is improved and the Al-rich intermetallic compound comprises greater than or equal to 50% of the continuous length of the layer. Preferably, the second Al-rich intermetallic compound layer has a quasi-continuous structure and occupies 50 to 90% of the continuous length of the layer. The proportion of the second Al-rich intermetallic compound layer is reduced from the conventional lower limit of 90% to 50% because a part of the Al-rich intermetallic compound originally used for forming the second layer in the plating layer also forms a new first Al-rich intermetallic compound layer. When a part of the second Al-rich intermetallic compound layer is fused with the first Al-rich intermetallic compound layer, the intermetallic compound in the second Al-rich intermetallic compound layer accounts for 50-75% of the continuous length of the layer.

(F) A surface layer: the composition of the surface layer is almost the same as the composition of the first intermediate layer and the second intermediate layer, and the layer contains, in weight percent: 35-47% of Fe, 50-61% of Al and 0-2% of Si. The layer also has less than 30% Al-rich intermetallic compound, typically between 2 and 15%, the layer comprising, in weight percent: 50-70% of Fe, 30-35% of Al and 2-6% of Si. There may also be a layer of pure aluminum or aluminum oxide with a continuity of 90% or more on the outer surface of the surface layer. Thus, after subdivision of the surface layer, the surface layer may be divided into 3 or more layers, which for ease of illustration, the present invention is consistent with conventional aluminized silicon hot-formed steel, collectively referred to as the surface layer.

It is noted that a continuous Al-rich intermetallic layer is present at the interface of the inter-diffusion layer and the first layer of the intermediate layer. The composition of the layer is the same as or similar to the first Al-rich intermetallic compound layer and the second layer.

More importantly, the coating has a 6-layer structure after thermoforming, crystal grains in the coating are finer, and grain boundaries of the coating are increased. After thermoforming, more grain boundaries in the coating are favorable for hydrogen in the steel matrix to diffuse out through the grain boundaries, and meanwhile, the discontinuous Al-rich intermetallic compound layer reduces the blocking effect on the internal requests of the matrix, so that the hydrogen embrittlement risk of the material is relieved. The refinement of the grains in the coating is related to the distribution of the Al-Si phase and Al-Si-Fe phase in the coating before thermoforming. When meeting the dispersion index requirement of the invention, the compatibility of the Al-Si phase and the Al-Si-Fe phase is easy to prevent the growth of the coating grains in the thermoforming heating process, thereby being beneficial to the grain refinement of the intermediate layer. Therefore, the Al-rich intermetallic compounds of the first layer and the second layer formed after thermoforming separate the intermediate layers of the first layer and the second layer, so that grains are finer, the toughness of the coating is further improved, the crack sensitivity is reduced, and the environmental tolerance of the coating can be improved. Also has the advantages of improving hydrogen embrittlement resistance, corrosion resistance and the like.

In some embodiments, the grain size of the first, second, and surface layers of the present invention is generally 30 μm or less; preferably, the grain size of the intermediate layer may satisfy 25 μm or less; preferably, the grain sizes of the first intermediate layer, the second intermediate layer, and the surface layer may be 20 μm or less. Further more preferably, the grain size of the first layer, the second intermediate layer, and the surface layer may be 15 μm or less.

The traditional hot forming steel does not have the distribution characteristics of the Al-Si phase and the Al-Si-Fe phase, the intermediate layer crystal grains of the coating after hot forming are coarse, the grain boundaries are few, and the intermetallic compound rich in Al is in a basically continuous state and has high continuity, so that the steel is unfavorable for diffusing hydrogen in the environment, has higher blocking effect on diffusing hydrogen and has higher hydrogen embrittlement sensitivity. Meanwhile, the coarse coating grains of the traditional hot forming steel, the basically continuous intermediate layer and the intermetallic compound layer rich in Al, so that the coating has higher brittleness.

It should be noted that by adjusting the thermoforming process, the inter-diffusion layer thickness can be varied, thereby reducing the intermediate layer thickness such that the coating exhibits less than 6 layers. However, the double-layer Al-rich intermetallic compound layer exists in the plating layer, and meets the requirement of the double-layer Al-rich intermetallic compound layer.

The structure of the coating formed by the invention can be detected and observed by a metallographic method. The thermoformed sample was cut into about 10mm by 20mm samples, with 20mm sides perpendicular to the rolling direction, which was the rolling direction of the steel substrate of the strip during cold rolling. The observation surface was a plated section of 20 mm. The sample was carefully polished to ensure that the surface layer was not damaged. The sample is soaked in 4% nitric alcohol for a certain period of time, such as 20 seconds, and the structural characteristics of the coating can be displayed under an optical microscope. Taking 1.0mm samples as an example, 50 samples are cumulatively tested, and the distance between each point is at least 50mm, namely, the condition that more than 1 sample is continuously taken on a component within the range of 50mm in radius is avoided as much as possible for testing. The section length of the coating observed under a microscope is equal to or more than 1000mm according to the section of the coating observed for each sample for 20 mm. Sampling at the edge of a component is avoided as much as possible, and when the component is large enough, the detection position of the sample is more than or equal to 50mm away from the edge; when the size of the component is insufficient, the component is as close to the middle position of the component as possible, or a plurality of components are adopted for verification. Of these samples, at least 1 sample exists, of which 1 field of view (1000 times) is provided with the bilayer Al-rich intermetallic compound layer of the invention, i.e. exhibits the 6-layer structural features of the invention. However, when the total length of the coating is not reached (the total length is equal to or greater than 1000mm in section length of the coating observed under a microscope for at least 50 samples), the 6-layer structure shown in fig. 3 is found in advance, and the material after thermoforming can be considered to meet the structural requirements of the invention. Generally, 50 samples are cumulatively tested (the cumulative length is that the section length of a coating layer which is totally and cumulatively observed on at least 50 samples is more than or equal to 1000mm under a microscope), the distance between each point is at least 50mm, and at least 5 samples exist, wherein each 1 view field (1000 times) is provided with the double-layer Al-rich intermetallic compound layer. Preferably, 50 samples are cumulatively tested, with a distance between each spot of at least 50mm, and at least 10 samples are present, with 1 field of view (1000 times) each provided with a bilayer Al-rich intermetallic layer according to the invention.

Because the detection range of the optical microscope is tiny, the actual structural characteristics of the coating are inconvenient to effectively reflect, the coating after thermoforming can be subjected to layered analysis by adopting a GDOES (glow discharge spectrometer), and the structural characteristics of the coating can be obtained from the distribution condition of the Al, si and Fe contents in the coating obtained by detection. Fig. 13 is a graph showing the concentration profile of the coating Si of the inventive member after thermoforming, and fig. 14 is a graph showing the concentration profile of the coating Si of the conventional member after thermoforming.

As shown in fig. 13, a lowest valley of Si concentration is found from the surface to the steel substrate, and a common tangent 1 and a common tangent 2 can be made to the left and right of the curve near the valley. Above these two common tangents, peaks 1, 2, 3 and 4 can be found that are far from the common tangents. There is a peak of Si concentration of surface oxidation in the range of about 0 to 0.2 μm from the surface, which is not one of the 4 peaks. The peak values are peak values of the difference value in the Y-axis with respect to the common tangent, that is, peak values formed by subtracting the common tangent concentration value in the common tangent region from the detected concentration. The lowest valley is typically the second valley, but may be the first or third valley. Similarly, a common tangent 1 and a common tangent 2 can be respectively made to the left and right of the curve near the second valley, and a peak 1, a peak 2, a peak 3 and a peak 4 with respect to the distance between the common tangents can be found above each diagonal.

The third peak may not be significantly affected by structural stability, as can be measured by increasing the sampling area of the GDOES. Taking a sample with a material thickness of 1.0mm as an example, when the single sampling diameter of GDOES is 4mm, 100 sampling points are detected cumulatively, and the distance between each point is at least 50mm, namely, the detection of more than 1 sample continuously taken within the range of 50mm radius by using GDOES is avoided as much as possible. Calculated according to the area of each detection point of 12.56mm ², namely the total detection area of at least 100 samples is larger than or equal to 1256mm ². Sampling at the edge of a component is avoided as much as possible, and when the component is large enough, the detection position of the sample is more than or equal to 50mm away from the edge; when the size of the component is insufficient, the component is as close to the middle position of the component as possible, or a plurality of components are adopted for verification. At least 1 sampling point is provided with the above-described peak 1, peak 2, peak 3 and peak 4 features of the present invention. Typically, when the single sampling diameter of the GDOES is 4mm, 100 sampling points are cumulatively detected, each at a distance of at least 50mm between each point, and at least 5 sampling points are present featuring peak 1, peak 2, peak 3 and peak 4 as described above in the present invention. Preferably, when the single sampling diameter of the GDOES is 4mm, 100 sampling points are cumulatively detected, each having a distance between them of at least 50mm, and at least 10 sampling points are provided with the above-described peak 1, peak 2, peak 3 and peak 4 features of the present invention. Preferably, when the single sampling diameter of the GDOES is 4mm, 100 sampling points are cumulatively detected, each having a distance between them of at least 50mm, and at least 20 sampling points are provided with the above-described peak 1, peak 2, peak 3 and peak 4 features of the present invention. Further preferably, when the single sampling diameter of the GDOES is 4mm, 100 sampling points are cumulatively detected, the distance between each point being at least 50mm, and at least 50 sampling points having the above-described peak 1, peak 2, peak 3 and peak 4 features of the present invention exist.

As shown in fig. 14, a lowest trough of Si concentration is found from the surface to the steel substrate, and a common tangent 1 can be made to the left of the curve near the trough. However, when a tangential point is found to the right near the valley, another significant tangential point is not found, except for a tangential point near the interface between the plating layer and the substrate. So above this common tangent 1 only peaks 1, 2 and 3 far from the common tangent can be found. There is a peak of Si concentration of surface oxidation in the range of about 0 to 0.2 μm from the surface, which is not one of the 3 peaks. The lowest valley is typically the second valley, but may also be the first valley. Likewise, a common tangent can be drawn to the right of the curve near the valley and peaks 1, 2 and 3 can be found. From outside to inside in microstructure, peak 1 corresponds to the Al-rich intermetallic compound in the surface layer, peak 2 corresponds to the Al-rich intermetallic compound layer, and peak 3 corresponds to the Al-rich intermetallic compound between the inter-diffusion layer and the intermediate layer (i.e., the inter-diffusion layer surface).

When GDOES is adopted for detection, the area of the accumulated detection should be equal to or larger than 1000mm ² generally, namely when the single sampling diameter of GDOES is 4mm, the accumulated detection exceeds 100 sampling points, and the distance between each point is at least 50mm, so that the detection requirement can be met. However, when the cumulative total area required for detection is not reached, but the characteristics are found in advance when 4 Si peaks as in fig. 13 are present, it is considered that the material after thermoforming also meets the structural requirements of the present invention.

The present invention has peaks of at least 4 Si concentrations, peak 1, peak 2, peak 3, peak 4, etc., from outside to inside in microstructure, peak 1 corresponding to the Al-rich intermetallic compound in the surface layer, peak 2 corresponding to the Al-rich intermetallic compound second layer, peak 3 corresponding to the Al-rich intermetallic compound first layer, and peak 4 corresponding to the Al-rich intermetallic compound between the interdiffusion layer and the intermediate first layer (i.e., interdiffusion layer surface). There is a peak of Si concentration of surface oxidation in the range of about 0 to 0.2 μm from the surface, which is not one of the 4 peaks. Therefore, the peak value 2 and the peak value 3 (double-layer Al-rich intermetallic compound layers) replace the traditional single-layer Al-rich intermetallic compound layers, so that the segregation of the Si concentration in the coating is reduced, the toughness of the coating is improved, the crack sensitivity of a steel substrate is improved, and the bending performance of the material is further improved. On the other hand, the double-layer Al-rich intermetallic compound layer with high Si concentration refines the plating crystal grains and simultaneously has the function of blocking the entry of elements of hydrogen, thereby further improving the hydrogen embrittlement resistance of the material. This is because both the fine plating grains and the double-layered high Si concentration Al-rich intermetallic compound layer are unfavorable for the diffusion of external hydrogen into the inside of the steel matrix during the hot forming process. While conventional single-layer Al-rich intermetallic compounds not only cause coarsening of the coating grains, but also the single-layer structure cannot block diffusion of hydrogen into the steel matrix.

For the surface layer after thermoforming, the present invention has the effect of migrating Al-rich intermetallic compounds in the surface layer inward so that the amount of Al-rich intermetallic compounds exposed or near the surface is reduced, and comparing fig. 13 and 14, it is clear that the peak Si concentration 1 in the coating layer after thermoforming of the present invention is up to 1.50 μm from the surface, whereas the peak Si concentration 1 in the coating layer after conventional thermoforming is about 0.25 μm from the surface. The change can obviously improve the structural compactness of the surface of the plating layer, and is beneficial to improving the toughness and hydrogen immersion resistance of the plating layer. It is apparent that the dense coating structure is also advantageous for improving the environmental corrosion resistance of the coating after thermoforming because less Al-rich intermetallic compound remains on the surface after inward migration of the Al-rich intermetallic compound of the surface layer of the invention, thereby reducing the number of effective primary cells formed by the Al-rich intermetallic compound and the nearby coating and reducing the rate of reflection of the coating in the environment. In the neutral salt spray test, the invention has more excellent corrosion resistance than the traditional coating. In general, the first peak (peak 1) of Si concentration in the coating of the present invention is at a position of 0.25 μm or more from the surface. Preferably, the first peak (peak 1) of Si concentration in the coating of the present invention is located at a distance of 0.45 μm or more from the surface. Preferably, the first peak (peak 1) of Si concentration in the coating of the present invention is located at a distance of 0.75 μm or more from the surface. Another method of calculating peak concentration is to obtain peak size data by subtracting the background, which can be done using related software (e.g., origin). After the back curve is obtained, the original data is subtracted from the back curve to obtain a required peak curve, and the influence of the peak condition on the material performance can be effectively evaluated by the method. For the convenience of calculation and explanation, the back curve of the invention is a common tangent line 1 and a common tangent line 2 which are cut below the plating layer Si concentration curve. Note that after subtracting the background, a small false peak exists at the lowest valley depth, which peak is caused by calculation, and occurs after the intersection of two common tangents deviates from the lowest valley, and the false peak should be removed without consideration. In general, the peak value after deducting the back reaches more than 4, and when the minimum peak value concentration value is more than or equal to 0.01%, the offset aggregation of the coating Si can be relieved, the toughness and hydrogen invasion resistance of the coating of the material are improved, and the corrosion resistance of the coating is obviously improved. Preferably, the peak value after deducting the back bottom reaches more than 4, and the minimum peak concentration value is more than or equal to 0.025%. Preferably, the peak value after deducting the back bottom reaches more than 4, and the minimum peak concentration value is more than or equal to 0.05%, so that the bending and hydrogen invasion resistance of the material can be effectively improved. Further preferably, the peak value after deducting the back bottom reaches more than 4, and the minimum peak concentration value is more than or equal to 0.25%, so that the bending and hydrogen invasion resistance of the material can be obviously improved. Since there is an error between the accuracy of each detection device, there is a gap in the detection results, but when the device accuracy is sufficient, the number of peaks present does not change.

When the thickness of the plating layer before thermoforming is less than 19 μm, the difficulty in forming the double Al-rich intermetallic compound layer of the invention in process control is increased, the thickness reduction of each layer is remarkable, and the hydrogen intrusion resistance is lowered, which is one of the reasons why the pre-plating layer of 19 μm or more is more recommended in the invention.

By reducing the thickness of the coating, the thickness of the surface layer can be removed or reduced, or the continuity of the surface layer is reduced, so that the coating has a 5-layer structure, but the double-layer middle layer and the double-layer Al-rich intermetallic compound layer also meet the requirements of the double-layer Al-rich intermetallic compound layer.

Preferably, the first Al-rich intermetallic compound layer occupies 1 to 50% of the length of the layer. The second Al-rich intermetallic compound layer accounts for more than or equal to 50 percent of the continuous length of the layer. More preferably. The second Al-rich intermetallic compound layer accounts for 50-90% of the continuous length of the layer.

In some embodiments, the component plating layer further includes a surface layer located outside the second Al-rich intermetallic layer.

In some embodiments, the first intermediate layer, the second intermediate layer, and the surface layer have a grain size of 30 μm or less. Preferably, the method comprises the steps of. The first intermediate layer, the second intermediate layer, and the grain size are 25 μm or less. More preferably, the first intermediate layer, the second intermediate layer, and the grain size are 15 μm or less.

In some embodiments, the component plating has a total thickness of 5 μm to 60 μm. Preferably, the total thickness of the member plating layer is 20 μm to 55 μm. Preferably, the total thickness of the member plating layer is 26 μm to 50 μm. Further preferably, the total thickness of the member plating layer is 30 μm to 50 μm.

heating the aluminized silicon steel or the precoated steel to an austenite region, wherein the heat preservation temperature is 880-950 ℃, and the heat preservation time is 3-15 minutes. The heating atmosphere is air, and the dew point is less than or equal to 0 ℃.

Specifically, the pre-coated steel plate is heated to an austenite region, the heat preservation temperature range is 880-950 ℃, and the heat preservation time is 3-15 minutes. The austenitizing furnace is filled with air, and the dew point in the austenitizing furnace is less than or equal to 0 ℃. Cooling the heat-preserving steel plate, taking out the heated steel plate from the furnace, transferring the heated steel plate to a punching machine for less than or equal to 10 seconds, then adopting a die to press down for deformation, and simultaneously cooling to below 200 ℃.

In the thermoforming process, aluminum flowers on the surface of the pre-plating layer can be decomposed, oxidized and restructured, and alloying can be carried out in the plating layer. However, aluminum patterns with the average area of more than or equal to 16mm ² are visible on the surface of the component after thermoforming, and are commonly called as 'ichthyosis'. The finishing process (also called leveling) after hot dip plating has a certain influence on the clarity of the aluminum flower after hot forming, and when the finishing elongation increases, the recognition of the aluminum flower after hot forming decreases. Also, the mold pressure during thermoforming has a large impact on the clarity of the aluminum flowers after thermoforming, and when the pressure increases, the recognition of the aluminum flowers decreases. The contact surface of the thermoformed component and the lower stamping die is also not suitable for identifying aluminum flowers. But after the surface is polished by sand paper (for example, the specification is 1200 meshes), the pattern appearance left by the aluminum flower after thermoforming can be seen. Or adjust the parameters of the light source to facilitate observation.

The total thickness of the coating of the component after thermoforming is 5-60 mu m. Preferably, the total thickness of the coating layer of the component after thermoforming is 20 μm to 55 μm. Preferably, the total thickness of the coating layer of the component after thermoforming is 26 μm to 50 μm. Further preferably, the total thickness of the coating layer of the member after thermoforming is 30 μm to 50 μm.

The technical solutions of the present invention will be clearly and completely described in the following in connection with the embodiments of the present invention. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Example 1

The steel substrate to be plated was provided with the following chemical composition, the material thickness was 1.5mm.

TABLE 1 chemical composition of the Steel matrix to be plated in% by weight

C	Si	Mn	P	S	Al	B	Cr	Ti	Nb	N
											0.36	0.49	1.09	0.012	0.0003	0.034	0.0033	0.33	0.018	0.022	0.0051

The steel substrate to be plated of table 1 was washed, dried, and then heated to a desired annealing temperature for heat preservation, in this example 800 c for 10 minutes.

The steel substrate to be plated of table 1 was cooled and the temperature of the steel substrate to be plated before entering the aluminum pot was controlled between 600 and 700 c, in this example 660 c.

The aluminum pot comprises the following components in percentage by mass: si: 8-11%; fe:1 to 4 percent; the balance of Al and unavoidable impurities. The aluminum pan of this example had a Si content of 10%, an iron content of 1.5% and the balance Al and unavoidable impurities.

And (3) removing redundant plating solution by adopting an air knife (a known technology) after hot dip plating of the steel substrate to be plated to obtain a pre-plated strip steel, wherein the thickness of a plating layer (a plating layer before thermoforming is called a pre-plating layer) of the strip steel is 25 mu m.

The cooling of the strip steel after hot dip aluminum silicon plating is carried out in two stages, and the first stage cooling is carried out after the strip steel is subjected to plating control until the strip steel is cooled to 570 ℃. The second cooling stage was carried out from 570 ℃ of strip until cooling to 300 ℃. The cooling rates are shown in table 2. And (3) cooling in a third stage: the strip was cooled from 300 c to room temperature using air and/or water.

Al-Si phase and Al-Si-Fe phase with steel coil number of 1-5 are coarse, and dispersion index is high. The Al-Si coating contains 20-40% of Al-Si phase including Al _nSi_m phase. Wherein n: m= (1.0 to 3.0): 1. the proportion of the Al _nSi_m phase in the Al-Si phase is more than or equal to 50 percent. ; the Al-Si-Fe phase with the proportion of 5-15% should be contained in the Al-Si coating. The Al-Si-Fe phase includes a Fe _aSi_bAl_c phase; wherein a is b and c= (1-2) 1 (4-9); the proportion of the Fe _aSi_bAl_c phase in the Al-Si-Fe phase is more than or equal to 50 percent.

The Al-Si phase and the Al-Si-Fe phase with the steel coil number of 6-7 are finer, and the dispersion index is lower. The Al-Si coating contains 5-30% of Al-Si phase including Al _nSi_m phase. Wherein n: m= (1.0 to 3.0): 1. the proportion of the Al _nSi_m phase in the Al-Si phase is more than or equal to 50 percent. ; the Al-Si-Fe phase with the proportion of 0.1-8% should be contained in the Al-Si coating. The Al-Si-Fe phase includes a Fe _aSi_bAl_c phase; wherein a is b and c= (1-2) 1 (4-9); the proportion of the Fe _aSi_bAl_c phase in the Al-Si-Fe phase is more than or equal to 50 percent.

The Al-Si phase and the Al-Si-Fe phase with the steel coil number of 8-10 are extremely fine, the dispersion index is low and the evaluation is difficult. The aluminum-silicon coating should contain small Al-Si phases with a proportion of less than or equal to 5 percent, or these small Al-Si phases are not effective evaluation objects. The Al-Si-Fe content in the Al-Si coating is very small, and these fine Al-Si phases are not effective evaluation targets.

TABLE 2 coating Cooling Rate and aluminum flower area

Fig. 1 is a typical surface aluminum pattern profile, and fig. 2 is a typical surface aluminum pattern trace profile after thermoforming. FIG. 11 is an aluminum flower area of 200mm ²,(200～400mm² or more); FIG. 12 is an aluminum flower area of 9mm ²(4～9mm² or less).

The aluminum flower area and the convexity of the aluminum flower of the steel coil number 8-10 are too small to meet the requirements of the invention. The convexities and the areas of the aluminum flowers with the numbers of 1 to 7 can meet the requirements of the invention.

It can be seen that the first stage cooling largely determines the size of the aluminum flower area, with the larger the cooling rate, the smaller the aluminum flower. The second stage has the same effect on the size of the plated aluminum flower, and the larger the cooling speed is, the smaller the aluminum flower is. The cooling rate of the second stage has less effect on the size of the flowers than the first stage.

Example 2

The steel substrate to be plated of table 1 was cooled and the temperature of the steel substrate to be plated before entering the aluminum pot was controlled to 660 ℃.

The aluminum pan of this example had a Si content of 10%, an iron content of 1.5% and the balance Al and unavoidable impurities.

And removing redundant plating solution by adopting an air knife after hot dip plating the steel substrate to be plated to obtain the pre-plated strip steel. The precoat thickness of the strip was controlled as shown in Table 3.

The cooling of the strip steel after hot dip aluminum silicon plating is carried out in two stages, wherein the first stage of cooling is carried out after the strip steel is subjected to plating control until the strip steel is cooled to 570 ℃, and the cooling speed is 10 ℃/s. The second stage of cooling was carried out from 570 ℃ until cooling to 300 ℃ at a cooling rate of 10 ℃/s. And (3) cooling in a third stage: the strip was cooled from 300 c to room temperature using air and/or water.

TABLE 3 precoating thickness and aluminum flower area

It can be seen that the thickness of the coating has a certain influence on the area of the aluminum flower, which is mainly that the thinner the coating is, the more nucleation sites are, and the more growth of aluminum flower dendrites is limited. In the comprehensive view, the thickness of the plating layer is more than 10 mu m, and the aluminum flower area is ideal; when the thickness of the coating is more than 19 mu m, the aluminum flower area is more stable; however, after exceeding 33. Mu.m, the growth of aluminum flower was not obvious.

Example 3

And removing redundant plating solution by adopting an air knife after hot dip plating the steel substrate to be plated to obtain the pre-plated strip steel. The precoated layer thickness of the strip steel is shown in Table 4.

The cooling of the strip steel after hot dip aluminum silicon plating is carried out in two stages, and the first stage cooling is carried out after the strip steel is subjected to plating control until the strip steel is cooled to 570 ℃. The second cooling stage was carried out from 570 ℃ of strip until cooling to 300 ℃. And (3) cooling in a third stage: the strip was cooled from 300 c to room temperature using air and/or water.

Heating the pre-plated steel plate to an austenite region, wherein the heat preservation range is 900 ℃, and the heat preservation time is 8 minutes. The austenitizing furnace is filled with air, the dew point in the austenitizing furnace is more than or equal to 0 ℃, the same dew point is controlled by each sample, and a certain amount of hydrogen is introduced into the austenitizing furnace. Cooling the heat-preserving steel plate, taking out the heated steel plate from the furnace, transferring the heated steel plate to a punching machine for less than or equal to 10 seconds, then adopting a die to press down for deformation and quenching, and cooling to below 200 ℃.

TABLE 4 ratio of first Al-enriched intermetallic compound layers to the layer and Performance results obtained for different coating thicknesses and aluminum flower areas

Note that: in the embodiment, in order to obtain the three-point bending angle and the four-point bending delay cracking time of the material, production process adjustment is specially carried out in experiments. The invention is only used for illustrating the improvement of the performance of the material, and does not represent the final service performance. The final service performance of the material is closely related to the thermoforming process. The material of the invention is helpful to improve the toughness and hydrogen embrittlement resistance of the material.

It can be seen from this: the larger the thickness of the plating layer is, the more favorable is for obtaining the first Al-rich intermetallic compound layer, so that the bending performance is improved, and the delayed cracking resistance is enhanced. The larger the aluminum flower area is, the more favorable is for obtaining the first Al-rich intermetallic compound layer, so that the bending performance is improved, and the delayed cracking resistance is enhanced. The plating layer is pressed down to be favorable for obtaining the first intermetallic compound layer rich in Al, and the stronger the delayed cracking resistance is.

Except that the T1 sample does not meet the requirement of the first Al-rich intermetallic compound layer of the invention, other samples meet the structural requirement of the hot forming thickness plating layer. The component plating after other sample thermoforming includes (a) an interdiffusion layer; (b) a first intermediate layer; (c) a first Al-rich intermetallic compound layer; (d) a second intermediate layer; (e) a second Al-rich intermetallic layer; (f) a surface layer.

The coating structure of the samples was analyzed after thermoforming. As shown in fig. 3, which is a coating diagram after T8 hot forming, the coating exhibits a typical coating 6-layer structure after hot forming of the hot formed steel of the present invention. As shown in fig. 4, which is a coating diagram after T9 thermoforming, the coating is a coating 4-layer structure after thermoforming of conventional hot-formed steel.

And 2% of stretching deformation is carried out on the T8 and the T9 which are formed by thermoforming, and the appearance of a coating crack is observed. FIG. 5 is a schematic representation of T8 of the present invention after hot forming and still deformed coating with a bilayer Al rich intermetallic hot formed steel. The inter-diffusion layer has better plasticity after deformation, and cracks can not penetrate through the inter-diffusion layer, but the steel matrix has cracks.

FIG. 6 is a schematic diagram of a coating layer of T9, which is deformed after conventional thermoforming, and which has only one layer of Al-rich intermetallic compound-based thermoformed steel. The inter-diffusion layer disintegrates after deformation, but the steel matrix is intact without cracks.

Fig. 8 shows the coating structure of the inventive member after thermoforming, wherein the double layer of Al-rich intermetallic compound separates the coating, the grains in the coating are finer and the fine grains in the coating. The average grain size is 25 μm or less.

Fig. 9 is a coating structure of a conventional thermoformed component after thermoforming, with coarse grains in the coating. The average grain size is 20 μm or more, and particularly the grains in the intermediate layer are coarse, and the maximum cross-sectional dimension may be more than 30 μm. The grains of the intermediate layer penetrate the majority of the coating, and the adverse effect of this coarse texture on coating performance is significant.

Example 4

Materials T14 to T17 with different dispersion indexes of the Al-Si and Fe-Al-Si phases of the coating required by the experiment are prepared by adopting the method of the invention, and the pre-coating samples are subjected to a thermoforming process. The thermal forming process adopted in the embodiment is that the temperature is 930 ℃ and the temperature is kept for 5 minutes. The austenitizing furnace is filled with air, the dew point in the austenitizing furnace is more than or equal to 0 ℃, the same dew point is controlled by each sample, and a certain amount of hydrogen is introduced into the austenitizing furnace.

And detecting the Si concentration of the coating on the sample by adopting GDOES, and obtaining the required Si concentration peak value data after deducting the back substrate. The coating structure, peak data and related performance results for these materials are shown in table 5.

It can be seen that the more advantageous the dispersion index of this example is for the formation of the Al-rich intermetallic compound layer of the bilayer required for the present invention, i.e., 4 Si concentration peaks occur. Further, higher Si concentration peaks are beneficial to improving the bending angle and the delayed cracking resistance of the material.

Samples T14 to T17 were studied using the neutral salt spray test method. The results indicated that all test samples developed a slight red rust after 2 hours; after 12 hours, the T14 red rust area is larger, about 80%; the area of T15 red rust is about 60%, and the areas of T16 and T17 red rust are about 50%. The samples were taken out and dried after 72 hours of salt spray test, and weight gain data per unit area of the samples were measured and shown in table 5. The unit area weight increasing reaction is the oxidation degree of the coating in an oxidation environment, namely the weight increasing condition after the coating obtains elements such as oxygen and the like. It can be seen that samples satisfying the 4 Si concentration peaks of the present invention have significantly lower weight gain due to oxidation than samples having 3 Si concentration peaks. Wherein the higher the minimum Si concentration peak value, the smaller the weight gain per unit area; when the minimum peak value of Si concentration exceeds 0.10%, the weight per unit area is increased to 2.7mg/cm ² or less. Therefore, after thermoforming, the corrosion resistance of the coating can be obviously improved by the complete 6-layer structure (4 Si concentration peaks).

TABLE 5 influence of different dispersion indices on coating and Properties

In the above technical solution of the present invention, the above is only a preferred embodiment of the present invention, and therefore, the patent scope of the present invention is not limited thereto, and all the equivalent structural changes made by the description of the present invention and the content of the accompanying drawings or the direct/indirect application in other related technical fields are included in the patent protection scope of the present invention.

The application discloses the following supplementary notes:

The supplementary note 1. An aluminized silicon steel is characterized by comprising a steel matrix and a pre-plating layer arranged on the steel matrix;

The pre-plating layer comprises an intermediate layer and an aluminum silicon plating layer; the nominal thickness of the aluminum silicon coating is 10-33 mu m; the aluminum silicon coating contains A l-S i phase with the proportion of 5-40% and A l-S i-F e phase with the proportion of 0.1-15%, and the dispersion index of the A l-S i phase and A l-S i-F e phase in the aluminum silicon coating is more than or equal to 0.05;

Wherein the mass fraction of silicon in A l-S i phase is 30-50%; the mass fraction of iron in A l-S i-F e phases is 10-35%, and the mass fraction of silicon is 3-15%.

The aluminized silicon steel according to appendix 2, characterized in that the aluminized silicon coating comprises A l-S i phase in a proportion of 10-30% and A l-S i-F e phase in a proportion of 0.1-10%.

The aluminized silicon steel according to appendix 1, characterized in that said A l-S i phases comprise a/n S/m phases; wherein n: m= (1.0 to 3.0): 1, a step of; the ratio of the AlnSim phase in A l-S i phase is more than or equal to 50%.

The aluminized silicon steel according to appendix 1, characterized in that the ai n S i m phase comprises at least one of A l 4S i 3 and A l 4S i 2.

Supplementary note 5 the aluminized silicon steel according to supplementary note 1, wherein the A l-S i-F e phases include F e a S i b A l c phases; wherein a is b and c= (1-2) 1 (4-9); the proportion of the Fe a S ib A l c phase in the A l-S i-F e phase is more than or equal to 50%.

Supplementary note 6 the aluminized silicon steel according to supplementary note 5, wherein the F e _a S i_b Al _c phases include fe si al ₄ phase and F e ₂S i A l₇ phase.

The additional mark 7 is characterized by comprising a steel matrix and a pre-plating layer arranged on the steel matrix; the pre-plating layer comprises an intermediate layer and an aluminum silicon plating layer;

The aluminum-silicon coating comprises aluminum flowers; the nominal thickness of the aluminum-silicon coating is 10-20 mu m, the aluminum flower meets the condition that a coordinate point formed by the aluminum flower area taking mm2 as a unit and the aluminum flower convexity taking mu m as a unit is positioned in a first convex pentagon, and the first convex pentagon is surrounded by five points (2, 3), (150,3), (350,7), (350, 35) and (2, 35).

The aluminized silicon steel according to the supplementary note 7, wherein the aluminum-silicon coating comprises aluminum flowers; the nominal thickness of the aluminum-silicon coating is 19-33 mu m, the aluminum flower meets the condition that a coordinate point formed by the aluminum flower area taking mm2 as a unit and the aluminum flower convexity taking mu m as a unit is positioned in a second convex pentagon, and the second convex pentagon is surrounded by five points (4, 5), (170,5), (400, 12), (400, 40) and (4, 40).

The aluminized silicon steel according to appendix 7, characterized in that the aluminized silicon coating comprises aluminum flowers; the nominal thickness of the aluminum-silicon coating is 10-20 mu m, the aluminum flower meets the condition that a coordinate point formed by aluminum flower convexity in mu m and aluminum flower border length in unit area of 1/mm is located in a third convex pentagon, and the third convex pentagon is surrounded by five points (0.1,7), (0.17,3), (10, 3), (10, 35), (0.1, 35).

The aluminized silicon steel according to the supplementary note 7, wherein the aluminum-silicon coating comprises aluminum flowers; the nominal thickness of the aluminum-silicon coating is 19-33 mu m, the aluminum flower meets the condition that the unit area aluminum lace boundary length taking 1/mm as a unit and a coordinate point formed by aluminum flower convexity taking mu m as a unit are positioned in a fourth convex pentagon, and the fourth convex pentagon is surrounded by five points (0.08, 12), (0.16,5), (8, 5), (8, 40) and (0.08, 40).

The method for preparing the aluminized silicon steel is characterized by comprising the following steps of:

Annealing the steel substrate to be plated, and then dip-plating in dip-plating liquid to obtain a dip-plated steel substrate; the dip coating liquid comprises the following components in percentage by mass: s i to 8 percent to 11 percent; f e:1 to 4 percent; the balance A l and unavoidable impurities;

Cooling the primary cold dip plated steel to 300 ℃ continuously at an average cooling rate of 5-25 ℃/s in a temperature regulating device under the condition of heating gas, and keeping the temperature for 2-30 seconds to obtain secondary cold dip plated steel; the temperature of the temperature regulating device is 300-570 ℃; the temperature of the heating gas is more than or equal to 100 ℃, and the total suspended particles of the gas is less than or equal to 0.2mg/m < 3 >;

The method for producing an aluminum-plated silicon steel according to the additional note 12, characterized in that the primary cold dip steel is obtained by cooling the dip steel substrate to 570 ℃ at a rate of 2 to 15 ℃/s and maintaining the temperature at 570 ℃ for 1 to 10 seconds.

The method for preparing aluminized silicon steel according to the supplementary note 13 is characterized in that the primary cold dip steel is cooled to 300 ℃ at an average cooling rate of 5-20 ℃/s, and the heat preservation time is 2-20 seconds, so as to obtain the secondary cold dip steel.

The supplementary note 14. The method for preparing aluminum-plated silicon steel according to any one of supplementary notes 11 to 13, wherein the annealing temperature in the annealing step of the steel substrate to be plated is 700 to 850 ℃, and the annealing time is 1 to 20 minutes; the temperature of the annealed steel matrix to be plated entering the immersion plating solution is 600-700 ℃.

The supplementary note 15. A precoated steel, characterized by that, the said precoated steel includes being cold rolled and/or polished by aluminized silicon steel; the precoated steel comprises a steel matrix and a finishing coating arranged on the steel matrix; the finishing coat is obtained by one of cold rolling and/or finishing;

The finishing coating comprises an intermediate layer and an aluminum-silicon coating; the nominal thickness of the aluminum silicon coating is 10-33 mu m; the aluminum silicon coating contains A l-S i phase with the proportion of 5-40% and A l-S i-F e phase with the proportion of 0.1-15%, and the dispersion index of the A l-S i phase and A l-S i-F e phase in the aluminum silicon coating is more than or equal to 0.05;

Supplementary note 16. A thermoformed component, characterized by, including steel substrate and component coating; the component coating is produced by interdiffusion between the steel substrate and an aluminum silicon precoat in a thermoforming process;

The member plating layer comprises an inter-diffusion layer, a first intermediate layer, a first A l-rich intermetallic compound layer, a second intermediate layer and a second A l-rich intermetallic compound layer which are sequentially stacked; the inter-diffusion layer is positioned at the innermost side of the component plating layer;

The intermetallic compound layer of the first A l is of a discontinuous structure, and the proportion of the intermetallic compound layer to the length of the layer is less than or equal to 80 percent; the second A l-rich intermetallic compound layer is of a quasi-continuous structure and occupies a continuous length proportion of more than or equal to 20 percent.

Supplementary note 17. The thermoformed article according to supplementary note 16, wherein the first A l-rich intermetallic layer is present in a proportion of 1 to 50% of the length of the layer; the intermetallic compound layer of the second A l accounts for more than or equal to 50 percent of the continuous length of the layer.

Supplementary note 18. The thermoformed article according to supplementary note 17, wherein the second A l-rich intermetallic layer comprises 50 to 90% of the continuous length of the layer.

Supplementary note 19. The thermoformed component according to any one of supplementary notes 16 to 18, wherein said component coating further comprises a surface layer located outside said second A l-rich intermetallic layer.

The thermoformed component according to appendix 20, wherein the average grain size of the first intermediate layer, the second intermediate layer, and the surface layer is 30 μm or less.

Supplementary note 21 the thermoformed component according to supplementary note 20, wherein the average grain size of the first intermediate layer and the second intermediate layer is 25 μm or less.

Supplementary note 22 the thermoformed article according to supplementary note 21, wherein the average grain size of the first intermediate layer and the second intermediate layer is 15 μm or less.

The thermoformed component according to any one of supplementary notes 23. The component coating has a total thickness of from 5 μm to 60. Mu.m.

Supplementary notes 24. The thermoformed component according to supplementary note 23, wherein the component coating has a total thickness of from 20 μm to 55. Mu.m.

The thermoformed component of appendix 25. The thermoformed component of appendix 24, wherein the component coating has a total thickness of from 26 μm to 50 μm.

The thermoformed component of appendix 26. The thermoformed component of appendix 25, wherein the component coating has a total thickness of from 30 μm to 50 μm.

Supplementary note 27. A thermoformed component comprising a steel substrate and a component coating; the component coating is produced by interdiffusion between the steel substrate and an aluminum silicon precoat in a thermoforming process;

the member plating layer has at least four S i concentration peaks in the thickness direction.

Supplementary note 28 the thermoformed component according to supplementary note 27, wherein said at least four S i concentration peaks comprise a first S i concentration peak, a second S i concentration peak, a third S i concentration peak and a fourth S i concentration peak from the component plating surface to the steel substrate;

The distance between the first S i concentration peak and the surface of the component plating layer is more than or equal to 0.25 mu m.

The thermoformed component according to appendix 29, characterized in that the distance between the first S i concentration peak and the component coating surface is not less than 0.45. Mu.m.

The thermoformed component of appendix 30. Appendix 29, wherein the first S i concentration peak is at a distance of 0.75 μm or more from the component coating surface.

The thermoformed component according to appendix 31. The thermoformed component according to appendix 30, characterized in that the first S i concentration peak is at a distance of 1.5 μm or more from the component coating surface.

The thermoformed component according to appendix 32, wherein said at least four S i concentration peaks have a concentration value of at least 0.01% after subtraction of the backing.

Appendix 33. The thermoformed component according to appendix 32, characterized in that the concentration value of the minimum peak is greater than or equal to 0.025%.

Appendix 34. The thermoformed component of appendix 33, wherein the concentration of the minimum peak is greater than or equal to 0.05%.

Additional notes 35. The thermoformed component of additional notes 34, wherein the concentration level of the minimum peak is greater than or equal to 0.25%.

Supplementary note 36. A process for producing a thermoformed component, comprising the steps of:

Heating the aluminized silicon steel according to any one of supplementary notes 1 to 10 or the precoated steel according to supplementary note 15 to an austenite region, wherein the heat preservation temperature is 880 to 950 ℃, and the heat preservation time is 3 to 15 minutes; the heating atmosphere is air, and the dew point is less than or equal to 0 ℃;

Supplementary note 37. A motor vehicle comprising the thermoformed component of any one of supplementary notes 16 to 35.

Claims

1. A thermoformed component comprising a steel substrate and a component coating; the component coating is produced by interdiffusion between the steel substrate and an aluminum silicon precoat in a thermoforming process;

the member plating layers have respective thicknesses corresponding to:

An Al-rich intermetallic compound in the surface layer,

A second layer of Al-rich intermetallic compound,

A first layer of Al-rich intermetallic compound,

At least four Si concentration peaks of Al-rich intermetallic compounds between the inter-diffusion layer and the intermediate first layer.

2. The thermoformed component according to claim 1, wherein said at least four peaks of Si concentration comprise a first peak of Si concentration, a second peak of Si concentration, a third peak of Si concentration, and a fourth peak of Si concentration from the component plating surface to the steel substrate;

3. The thermoformed component according to claim 2, wherein said first peak Si concentration is at a distance of 0.45 μm or more from the component coated surface.

4. A thermoformed component according to claim 3, wherein said first peak Si concentration is at a distance of 0.75 μm or more from the component coating surface.

5. The thermoformed component according to claim 4, wherein said first peak Si concentration is at a distance of 1.5 μm or more from the component coated surface.

6. The thermoformed component according to claim 1, wherein said at least four peaks of Si concentration have a concentration value of at least 0.01% after subtraction of the back side.

7. The thermoformed component of claim 6, wherein said minimum peak concentration value is greater than or equal to 0.025%.

8. The thermoformed component according to claim 7, wherein said minimum peak concentration value is greater than or equal to 0.05%.

9. The thermoformed component according to claim 8, wherein said minimum peak concentration value is greater than or equal to 0.25%.

10. The thermal forming member according to any one of claims 1 to 9, wherein the method of obtaining the at least four Si concentration peaks includes:

and finding a lowest valley value of Si concentration between the component coating and the steel matrix, respectively making two common tangent lines to the left and right of the curve at the valley value, and finding a first Si concentration peak value, a second Si concentration peak value, a third Si concentration peak value and a fourth Si concentration peak value which are far away from the common tangent lines above the two common tangent lines.

11. The thermoformed component of claim 10, wherein said at least four peaks of Si concentration do not include peaks of Si concentration at surface oxidation in the range of 0-0.2 μm from the surface.

12. A motor vehicle comprising a thermoformed component according to any one of claims 1 to 11.