CN113436687B - Method for rapidly judging alloying degree of aluminum or aluminum alloy coating - Google Patents
Method for rapidly judging alloying degree of aluminum or aluminum alloy coating Download PDFInfo
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Classifications
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- G—PHYSICS
- G16—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR SPECIFIC APPLICATION FIELDS
- G16C—COMPUTATIONAL CHEMISTRY; CHEMOINFORMATICS; COMPUTATIONAL MATERIALS SCIENCE
- G16C20/00—Chemoinformatics, i.e. ICT specially adapted for the handling of physicochemical or structural data of chemical particles, elements, compounds or mixtures
- G16C20/10—Analysis or design of chemical reactions, syntheses or processes
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- G—PHYSICS
- G16—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR SPECIFIC APPLICATION FIELDS
- G16C—COMPUTATIONAL CHEMISTRY; CHEMOINFORMATICS; COMPUTATIONAL MATERIALS SCIENCE
- G16C20/00—Chemoinformatics, i.e. ICT specially adapted for the handling of physicochemical or structural data of chemical particles, elements, compounds or mixtures
- G16C20/20—Identification of molecular entities, parts thereof or of chemical compositions
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- Chemical & Material Sciences (AREA)
- Bioinformatics & Cheminformatics (AREA)
- Crystallography & Structural Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Bioinformatics & Computational Biology (AREA)
- Computing Systems (AREA)
- Theoretical Computer Science (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Physics & Mathematics (AREA)
- Analytical Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Coating With Molten Metal (AREA)
Abstract
The invention discloses a method for rapidly judging the alloying degree of an aluminum or aluminum alloy coating, which is used for judging the alloying degree of the coating by combining the numerical values of L, a and b in the color space of Hunter L, a and b of the coating with an alloying window.
Description
Technical Field
The invention relates to a method for rapidly judging the alloying degree of an aluminum or aluminum alloy coating.
Background
In recent years, as the requirements on safety, energy conservation and emission of automobiles are increasingly strict in various countries in the world, the weight reduction and the improvement of the safety performance of automobiles are the focus of attention in the automobile industry. Generally, the high-strength steel can be used for realizing light weight and improving safety performance, but the high-strength steel has the problems of high rebound, difficult forming and the like in the traditional cold stamping mode. In this case, the hot stamping technique is complete. The hot stamping technology realizes high strength of the product by combining austenitizing treatment, high-temperature forming and rapid cooling, improves the forming performance of the product and has smaller rebound.
In the hot stamping forming process, if bare plate hot forming steel is adopted, protective gas such as nitrogen or argon is introduced into a heating furnace to avoid iron scale and decarburization, but oxidation is inevitably generated in the discharging and feeding and hot stamping processes, the generated iron scale reduces the adverse effect of the heat exchange coefficient between a die and a plate on the product performance, increases the friction coefficient between the plate and the die, and aggravates the die abrasion. More importantly, the hot stamping of the bare board generally requires shot blasting to ensure good surface quality, and the shot blasting reduces the dimensional accuracy of the part. In order to avoid the problems, the hot forming steel coated with the coating becomes a main stream product in the current market, the hot forming steel coated products developed at home and abroad at present mainly comprise aluminum silicon (Al-Si), pure zinc (GI), zinc-iron alloy (GA), zinc-nickel (Zn-Ni) and the like, and the Zn-based coated hot forming steel is easy to generate liquid zinc to cause brittleness during high-temperature stamping, so that stamping cracking is caused, and the coating products which are already applied at present mainly comprise Al-Si.
The aluminum-silicon coating and the matrix are mutually diffused in the heating process to form an Fe-Al and Fe-Al-Si alloying coating, namely the coating is subjected to an alloying process, and the improvement of the alloying degree is shown by the continuous increase of the iron content in the coating. Different final coating alloying degrees of different thermoforming processes may form different coating structures and coating components, which are closely related to the coating performance, welding performance and the like of the product. It is found that when the temperature is low or the heating time is short, the alloying degree of the coating is low or even the coating is not completely alloyed, the surface roughness of the coating is possibly low, the paint adhesion is reduced, the coating performance is deteriorated, a certain heating temperature and heating time are required to be ensured to ensure the complete austenitization of the substrate, a certain alloying degree is achieved at this time, and in general, the thicker the thickness of the aluminum or aluminum alloy coating is, the higher the thermal reflectivity of the material is, and the complete austenitization time of the substrate is longer. However, as the heating temperature is increased or the heating time is prolonged, the higher the alloying degree of the coating is, more holes are formed in the coating, and the coating is more likely to peel off and enter the welding seam in the welding process, so that the welding performance is reduced.
Patent CN101583486B (hereinafter referred to as patent 1) provides a coated steel strip and hot stamped products prepared therefrom.
The precoat in patent 1 has a four-layer structure after hot stamping, and the microstructure from the substrate to the surface is as follows: an inter-diffusion layer (average composition: 86-95% Fe, 4-10% Al, 0-5% Si), an intermediate layer (average composition: 39-47% Fe, 53-61% Al, 0-2% Si), an intermetallic compound layer (average composition: 62-67% Fe, 30-34% Al, 2-6% Si), a surface layer (average composition: 39-47% Fe, 53-61% Al, 0-2% Si), the total coating thickness being greater than 30 μm, the inter-diffusion layer having a thickness of less than 15 μm, the intermetallic compound layer and the surface layer being at least 90% horizontal and quasi-continuous with less than 10% intermetallic compound layer present at the outermost surface of the product.
Patent CN108588612B (hereinafter referred to as patent 2) provides a hot-dip press formed member, a pre-coated steel sheet for hot-dip press forming, and a hot-dip press forming process.
In the patent 2, after hot stamping, the precoat is formed from a substrate to the surface by one layer, two layers, three layers or four layers, wherein one layer (an inter-diffusion layer: alpha Fe containing Al and Si, the Fe content is more than or equal to 70%, 6-14 μm), two layers (a first layer is an inter-diffusion layer: alpha Fe containing Al and Si, the Fe content is more than or equal to 70%, 6-14 μm), a second layer is an intermetallic compound layer: fe, al and Si, the Fe content is 30% -47.9%, 0-8 μm), three layers (a first layer is an inter-diffusion layer: alpha Fe containing Al and Si, the Fe content is more than or equal to 70%, 6-14 μm), a second layer is an intermetallic compound layer: fe, al and Si, the Fe content is 30% -47.9%, 0-8 μm, a third layer is an intermetallic compound layer: fe, al and Si, the Fe content is 48% -69%, 0-10 μm), the four layers (a first layer: al and Si, the first layer: 0% -10 μm), the second layer: 0% -4%, the third layer is an intermetallic compound layer: 0% -10%, the fourth layer: 0% -4%, the volume% is at least equal to 30% -10%, the third layer is a third layer, the volume% of the inter-0% of the inter-metallic compound layer is 0% and the volume% of the structure is at least equal to 0% -4% of the third layer.
In both patent 1 and patent 2, the structure and composition of the coating after hot stamping of the pre-coated aluminum or aluminum alloy coated steel sheet are limited, the alloying degree of the aluminum or aluminum alloy coating is a key index for judging whether the hot stamped product of the aluminum or aluminum alloy coated steel sheet is qualified, generally the alloying degree of the aluminum or aluminum alloy coating can be judged by the structure and composition of the coating after hot stamping, and the coating structure and the coating composition can be analyzed by means of physical detection equipment such as an optical microscope, a scanning electron microscope, a glow spectrum analyzer, and the like. However, in the actual operation process, the judging method needs to be subjected to a series of complex procedures such as sampling, sample preparation, detection and the like, the analysis difficulty is high, the detection accuracy of a coating structure and a coating component is greatly influenced by the sample preparation level and the accuracy of analysis equipment, the time consumption is long, when the thermal forming production line has process abnormality such as large temperature fluctuation or overlong heating time, the alloying degree of the aluminum or aluminum alloy coating fluctuates at the moment, the judging method is low in efficiency, the judgment of the alloying degree of the product coating cannot be rapidly carried out, and the production rhythm is greatly reduced.
Therefore, how to quickly judge the alloying degree of the aluminum or aluminum alloy coating is important to improve the hot stamping production efficiency of the steel plate with the pre-coated aluminum or aluminum alloy coating.
Disclosure of Invention
The invention aims to provide a method for rapidly judging the alloying degree of an aluminum or aluminum alloy coating, and the method uses detection equipment with lower price, simple and convenient operation and higher efficiency. The problems of complex procedures, high analysis difficulty, low efficiency and the like existing in the conventional judgment of a coating structure, coating components and the like after hot stamping can be solved.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
A method for rapidly judging the alloying degree of an aluminum or aluminum alloy coating judges the alloying degree of the coating by combining the values of L, a and b in the Hunter L, a and b color spaces of the coating with an alloying window.
The coating is formed by interdiffusion of a precoated coating and base steel after a precoated aluminum or aluminum alloy coated steel plate is heated. The thickness of the precoating coating is 3-33 mu m. The total thickness of the precoated aluminum or aluminum alloy steel plate is 0.4-3.0 mm.
The base steel can be selected to be any steel grade.
The heating mode of the pre-coated aluminum or aluminum alloy coated steel sheet may be selected from resistance heating, radiation heating or induction heating, and is not limited to the above mode, and the heating may be followed by hot stamping or other heat treatment operations.
Specifically, when L is more than or equal to 42, the coating is underalloyed;
When the thickness of the precoating coating is more than or equal to 3 mu m and less than or equal to 19 mu m, when L is less than or equal to 35 and a is less than or equal to 1 and b is less than or equal to 1, the coating is suitable alloyed or underalloyed; when L is more than 35 and less than 42, a is less than or equal to 1, b is less than or equal to 1, and the coating is under-alloyed or over-alloyed; when L < 42 and a > 1 or b > 1, the coating is overalloyed;
When the thickness of the pre-coating is more than 19 mu m and less than or equal to 33 mu m, when L is less than or equal to 35 and a is more than 1 or b is more than 1, the coating is under-alloyed; when L is less than 42 and a is less than or equal to 1 and b is less than or equal to 1, the coating is properly alloyed; when 35 < L < 42 and a > 1 or b > 1, the coating is under-alloyed or over-alloyed.
A method of judging that the coating is properly alloyed or under-alloyed when L.ltoreq.35 and a.ltoreq.1 and b.ltoreq.1 when the thickness of the precoated coating is 3 μm or less and 19 μm or less and judging that the coating is under-alloyed or over-alloyed when 35 < L < 42 and a.ltoreq.1 and b.ltoreq.1: the temperature and time during the alloying reaction, namely the alloying process window. Suitable alloying windows (i.e. coordinate spaces defined by heating temperatures and heating times) are within the pattern ABCD defined in fig. 7 and the pattern EFGH, specifically if the total steel thickness of the pre-coat is greater than or equal to 0.4mm and less than or equal to 1.5mm, the temperatures and times are defined within the pattern ABCD having time and temperature coordinates defined by a (2.5 min,930 ℃) B (5.5 min,930 ℃) C (12.5 min,880 ℃) D (4 min,880 ℃) if the total steel thickness of the pre-coat is greater than 1.5mm and less than or equal to 3.0mm, the temperatures and times are defined within the pattern EFGH having time and temperature coordinates defined by E (3.5 min,940 ℃) F (7.5 min,940 ℃) G (12.5 min,900 ℃) H (6 min,900 ℃). The coating is under-alloyed if the heating temperature or heating time of the alloying is lower than the heating temperature or heating time defined by the alloying process window, the coating is suitably alloyed if the heating temperature or heating time of the alloying is within the alloying process window, and the coating is over-alloyed if the heating temperature or heating time of the alloying is higher than the heating temperature or heating time defined by the alloying process window.
A method for judging the coating layer to be under alloyed or over alloyed when 35 < L < 42 and a > 1 or b > 1 when the thickness of the pre-coated coating layer is more than 19 μm and less than or equal to 33 μm: the temperature and time during the alloying reaction, namely the alloying process window. Suitable alloying windows (i.e. coordinate spaces defined by heating temperatures and heating times) are within the pattern IJKL and the pattern MNOP defined in fig. 8 when the thickness of the pre-coating layer is greater than 19 μm and less than or equal to 33 μm, specifically, if the total thickness of the steel of the pre-coating layer is greater than or equal to 0.4mm and less than or equal to 1.5mm, the temperatures and times are defined within the pattern IJKL having time and temperature coordinates defined by I (3 min,930 ℃), J (6 min,930 ℃), K (13 min,880 ℃), L (4.5 min,880 ℃), if the total thickness of the steel of the pre-coating layer is greater than 1.5mm and less than or equal to 3.0mm, the temperatures and times are defined within the pattern MNOP, and the pattern MNOP has time and temperature coordinates defined by M (4 min,940 min, N (940 ℃), O (13 min,900 ℃), P (6.5 min,900 ℃). The coating is under-alloyed if the heating temperature or heating time of the alloying is lower than the heating temperature or heating time defined by the alloying process window, and the coating is over-alloyed if the heating temperature or heating time of the alloying is higher than the heating temperature or heating time defined by the alloying process window.
The plating solution for forming the precoating coating comprises the following components in percentage by weight: 8-11% of Si, 2-4% of Fe and the balance of aluminum and unavoidable impurities.
The aluminum or aluminum alloy coating (taking an aluminum silicon coating as an example) is pre-coated, an intermetallic compound layer (Fe 2Al5、Fe2SiAl7) and an aluminum coating are respectively arranged from the side to the surface of the substrate, when the aluminum or aluminum alloy coating is heated, fe 2SiAl7 reacts with the aluminum coating to generate a liquid phase, si rapidly diffuses into the liquid phase coating to form a Si-rich Fe-Al-Si layer (different from Fe 2SiAl7), fe-Al alloy phases are formed at two sides of the Fe-Al-Si layer, the side close to the substrate is converted into a diffusion layer (Fe and Fe 3 Al) due to strong diffusion of Fe and Al, and the coating structure sequentially comprises a diffusion layer, a Fe-Al-Si layer and a Fe-Al layer from the substrate to the surface. Continuing heating, thickening the diffusion layer and the Fe-Al-Si layer, thinning the Fe-Al layer, gradually reducing the number of coating layers, and firstly, possibly converting the coating structure into the diffusion layer, the Fe-Al-Si layer and a discontinuous surface layer, wherein the discontinuous surface layer is a mixed structure of Fe-Al and Fe-Al-Si; continuing alloying, and converting the coating structure into a diffusion layer, a Fe-Al layer and a Fe-Al-Si layer or into a diffusion layer, a Fe-Al-Si layer and a discontinuous surface layer, wherein the discontinuous surface layer is a mixed structure of Fe-Al and Fe-Al-Si; the alloying degree is further improved, and the coating structure is converted into a diffusion layer and a Fe-Al-Si layer; continuing the alloying, the coating consists of only the diffusion layer. It should be noted that the diffusion layer, the Fe-Al layer, and the Fe-Al-Si layer all contain Fe, al, and Si, except that the different element ratios are, in general, 80% by weight or more of Fe, 5% by weight or less of Si, the balance being Al, 30% by weight to 50% by weight of Fe, 2% by weight or less of Si, the balance being Al, 55% by weight to 79% by weight of Fe, 2% by weight or more of Si, and the balance being Al in the Fe-Al-Si layer.
When the alloying degree of the coating is proper alloying, when the thickness of the precoating coating is more than or equal to 3 mu m and less than or equal to 19 mu m, the coating structure sequentially comprises a diffusion layer, a Fe-Al-Si layer and a continuous or discontinuous surface layer from the substrate to the surface, wherein the continuous surface layer is the Fe-Al layer, and the discontinuous surface layer is a mixed structure of Fe-Al and Fe-Al-Si.
When the alloying degree of the coating is proper alloying, the thickness of the precoated coating is more than 19 mu m and less than or equal to 33 mu m, and the coating structure sequentially comprises a diffusion layer, a Fe-Al-Si layer and a Fe-Al layer from the substrate to the surface.
When the coating is underalloyed, there is an aluminum coating or Fe 2SiAl7 that is not completely transformed on the outermost surface of the coating after heating.
When the coating is overalloyed, the coating structure sequentially comprises a diffusion layer, a Fe-Al layer and an e-Al-Si layer, or a diffusion layer, a Fe-Al-Si layer and a discontinuous surface layer, or a diffusion layer and a Fe-Al-Si layer, or only a diffusion layer from the substrate to the surface when the thickness of the precoated coating is more than or equal to 3 mu m and less than or equal to 19 mu m, wherein the discontinuous surface layer is a mixed structure of Fe-Al and Fe-Al-Si, and the diffusion layer is Fe and Fe 3 Al.
When the coating is in overalloying, the thickness of the precoated coating is more than 19 mu m and less than or equal to 33 mu m, the coating structure is still in a four-layer structure, and a diffusion layer, a Fe-Al-Si layer and a Fe-Al layer are sequentially arranged from the substrate to the surface. It should be noted that when the heating temperature is too high, e.g., greater than 1000 c, and the heating time is too long, e.g., greater than 15min, the coating structure is also transformed from a four-layer structure when the pre-coat coating thickness is greater than 19 μm and less than or equal to 33 μm.
When the coating is overalloyed, the number and size of holes in the coating increases rapidly, whether the thickness of the pre-coated coating is greater than or equal to 3 μm and less than or equal to 19 μm or greater than 19 μm and less than or equal to 33 μm. The voids are believed to be due to the different rates of interdiffusion of the aluminum coating and the iron matrix. The inventor researches find that when a large number of holes appear in the coating and the hole size is large (for example, the number of holes in each 1000 mu m 2 is more than 0.5 mu m is not less than 10), the coating is easy to peel off at the holes and adhere to the welding electrode during welding, so that the abrasion of the welding electrode is increased and the welding performance is obviously reduced.
The inventor has found through intensive research that after the precoated aluminum or aluminum alloy coating is formed by hot stamping, the color of the coating is changed, the color change of the coating is mainly a series of oxidation behaviors of elements such as Fe, al and the like on the surface, the color change mainly occurs in the heating process of a heating furnace, the temperature of a material sheet is lower and the time is shorter in the process from the heating furnace to the completion of hot stamping, the color change of the coating is smaller, and the color change of the coating is regular. The heating temperature of the hot forming of the aluminum or aluminum alloy coating is generally not more than 1000 ℃ and the heating time is not more than 15min, the invention develops the research on the color transformation rule of the coating after heating in the heating temperature and heating time interval, and along with the improvement of the alloying degree of the coating, the color of the coating is sequentially transformed as follows: silver white, blue, yellow, red, the color of the coating changes faster as the thickness of the coating increases. It has also been found that there may be a transition color between the colors, such as a light blue between blue and yellow (blue being the primary color and yellow being the secondary color), and that the coating has a suitable coating structure, coating composition when the coating color is blue or between blue and yellow, and that the coating is under-alloyed or over-alloyed when the coating color is between silver and blue or Huang Gongshi, i.e. the coating structure, coating composition can be well mapped by the coating color detection.
At present, three main methods exist for color detection: the visual method has a certain subjective color, the measurement result has low precision and low measurement efficiency, the photoelectric integration method simulates the tristimulus value characteristics of human eyes, the tristimulus value of the color is directly measured by using the photoelectric integration effect, and the spectrophotometry is used for obtaining the tristimulus value of the color by measuring the spectral power distribution of a light source or the spectral power of reflected light of an object, so that various color parameters are calculated. It should be noted that the present invention is not limited to the above method, and any method that does not depart from the spirit of the present invention is intended to be encompassed by the present invention.
In the technical scheme of the invention, the color detection is illustrated by taking spectrophotometry as an example, and is performed by adopting Hunter L, a and b color spaces, wherein L represents the brightness of an object: 0 to 100 represents black to white, and a represents red and green of an object: positive values represent red, negative values represent green, 0 represents neutral, and b represents the yellow-blue color of the object). Positive values indicate yellow, negative values indicate blue, and 0 indicates neutral. Specifically, the color exhibited by an object is the combined effect of the values of L, a, b: the greater the L value, the greater the object brightness, and the smaller the L value, the less the object brightness; the more red the object is when the value of a is positive and is greater, at this time when the absolute value of b is less than the value of a, the more red the object is mainly in the color represented by the value of b (yellow or blue) when the absolute value of b is greater than the value of a, the more green the object is when the value of a is negative and is less, at this time the more green the object is mainly in the color represented by the value of b (yellow or blue) when the absolute value of b is less than the absolute value of a, and the more than the absolute value of b is in the color represented by the value of b; the more yellow the object is when the value of b is positive and is greater, the more yellow the object is when the absolute value of a is less than the value of b, the more yellow the object is mainly represented by the value of a (green or red) when the absolute value of a is greater than the value of b, the more blue the object is when the value of b is negative and is less, the more blue the object is mainly represented by the value of a when the absolute value of a is less than the absolute value of b, and the more blue the color the object is mainly represented by the value of a (green or red) when the absolute value of a is greater than the absolute value of b.
The inventors conducted studies on the color transition of the coating with different pre-coating thicknesses along with the heating time, and adopted the pre-coating thicknesses from low to high to be 5 mu m (thin coating), 19 mu m (middle thickness coating) and 33 mu m (thick coating), the transition of the L, a and b values of the coating is regular, and the L value is larger, generally equal to or greater than 42 at the moment when the alloying degree of the coating is lower, the L value is in a descending trend along with the improvement of the alloying degree of the coating, the L value is smaller when the coating is in a blue color, the alloying degree is continuously improved, the color of the coating is gradually changed to yellow-red, and the L value is in a slow ascending trend, as shown in fig. 1, fig. 2, fig. 3 and fig. 4. When the thickness of the precoating coating layer is thin, the L value is generally not more than 35 when the thickness is not less than 3 mu m and not more than 19 mu m, the coating layer has a proper coating structure and a proper coating composition, namely, a proper alloying degree, and when the thickness is thick, the L value is generally not more than 42 when the thickness is not less than 19 mu m and not more than 33 mu m, the coating layer has a proper coating structure and a proper coating composition, namely, a proper alloying degree.
When L is more than or equal to 42, the coating is necessarily under-alloyed, and when L is less than 42, the coating is possibly under-alloyed, proper alloying or over-alloyed, and the degree of alloying of the coating is judged to be carried out by combining the a value and the b value of the coating.
When the precoating is different in coating thickness, when the alloying degree of the coating is low (under-alloying), the color parameters a and b show different changes, when the precoating coating is thinner, the color of the coating is mainly changed from silvery white to dark red when the thickness of the precoating coating is more than or equal to 3 mu m and less than or equal to 19 mu m, the values of a and b are smaller at the moment, the value of a is generally less than or equal to 1, the value of b is between-1 and 1, but when the thickness of the precoating coating is thicker, the color of the coating is changed from silvery white to yellow when the thickness of the precoating coating is more than or equal to 19 mu m and the value of a and b is generally greater than 1 or the value of b is greater than 1. The method is characterized in that when the alloying degree of the coating is continuously improved, the b value is smaller and is generally in a negative value interval, the alloying degree of the coating is further improved, the color of the coating is gradually changed to yellow red, the a and b values are gradually increased, the thicker the precoat layer is, the faster the color is changed, when the thickness of the precoat layer is more than or equal to 3 mu m and less than or equal to 33 mu m, at the moment, the a and b values are generally less than or equal to 1, the coating has proper coating structure and coating composition, and when a is more than 1 or b is more than 1, the coating is overalloyed.
When the thickness of the pre-coating layer is more than or equal to 3 mu m and less than or equal to 19 mu m, L is less than 42 when a is more than 1 or b is more than 1, and the coating layer is overalloyed.
When the thickness of the pre-coating is more than or equal to 3 mu m and less than or equal to 19 mu m, when a is less than or equal to 1 and b is less than or equal to 1, the coating may be underalloyed, properly alloyed or overalloyed, and the judgment of the alloying degree of the coating is carried out by combining the L value of the coating. At this time, the L value may be 42 or more or less, if L is 42 or more, the coating is under-alloyed, if L is 35 or less, the coating is under-alloyed or suitably alloyed, if 35 < L < 42, the coating is under-alloyed or over-alloyed. The method for judging the underalloyed, proper alloyed or overalloyed coating comprises the following steps: according to the temperature and time of alloying reaction. Suitable alloying windows (i.e. coordinate spaces defined by heating temperatures and heating times) are defined by figure 7 within the graphic ABCD and graphic EFGH, i.e. within the alloying process window, when the pre-coat layer thickness is equal to or greater than 3 μm, specifically if the total steel thickness of the pre-coat layer is equal to or greater than 0.4mm and equal to or less than 1.5mm, the temperatures and times are defined within the graphic ABCD, which has time and temperature coordinates defined by a (2.5 min,930 ℃), B (5.5 min,930 ℃), C (12.5 min,880 ℃), D (4 min,880 ℃), and if the total steel thickness of the pre-coat layer is equal to or greater than 1.5mm and equal to or less than 3.0mm, the temperature and time are defined within the graphic EFGH, which has time and temperature coordinates defined by E (3.5 min,940 ℃) F (7.5 min,940 ℃) and G (12.5 min, 900H (6 min,900 ℃)). The coating is under-alloyed if the heating temperature or heating time of the alloying is lower than the heating temperature or heating time defined by the alloying process window, the coating is suitably alloyed if the heating temperature or heating time of the alloying is within the alloying process window, and the coating is over-alloyed if the heating temperature or heating time of the alloying is higher than the heating temperature or heating time defined by the alloying process window.
When the precoat layer thickness is greater than 19 μm and less than or equal to 33 μm, when a.ltoreq.1 and b.ltoreq.1, L < 42, the coating is suitably alloyed.
When the thickness of the pre-coating layer is more than 19 mu m and less than or equal to 33 mu m, when a is more than 1 or b is more than 1, the coating layer is under-alloyed if L is less than or equal to 35, and when L is more than 35 and less than 42, the coating layer is under-alloyed or over-alloyed. The method for judging the coating to be under alloyed or over alloyed comprises the following steps: according to the temperature and time of alloying reaction. At a precoat coating thickness of greater than 19 μm and less than or equal to 33 μm, a suitable alloying process window (i.e., a coordinate space defined by a heating temperature and a heating time) is within the pattern IJKL defined in fig. 8 and the pattern MNOP, i.e., within the alloying process window, the coating after heating has a suitable coating structure, specifically, if the total steel thickness of the precoat coating is 0.4mm or more and 1.5mm or less, the temperature and time are defined within the pattern IJKL having time and temperature coordinates defined by I (3 min,930 ℃), J (6 min,930 ℃), K (13 min,880 ℃), L (4.5 min,880 ℃), and if the total steel thickness of the precoat coating is greater than 1.5mm and 3.0mm or less, the pattern MNOP has a temperature and temperature coordinates defined by M (4 min,940 ℃) O (4 min,940 ℃) and P (6 min,900 ℃) of P (5 min, 900). The coating is under-alloyed if the heating temperature or heating time of the alloying is lower than the heating temperature or heating time defined by the alloying process window, and the coating is over-alloyed if the heating temperature or heating time of the alloying is higher than the heating temperature or heating time defined by the alloying process window.
In the technical scheme of the invention, the inventors sum up the range of values of L, a and b under different precoating thicknesses and different alloying degrees by counting the corresponding relation between the values of L, a and b in Hunter L, a and b color spaces of the coating after heating and stamping of the coated aluminum or aluminum alloy coated steel plate and the alloying degree of the coating in the actual production process. And then when the alloying degree of the coating is judged, the alloying degree of the coating can be directly judged by combining the color of the coating with an alloying window, and the method is simple, convenient and quick.
Compared with the conventional method for judging the alloying degree of the coating after hot stamping of the pre-coated aluminum or aluminum alloy coated steel plate through a coating structure, a coating component and the like after hot stamping, the method has the advantages of complex process, high analysis difficulty and low efficiency.
Drawings
FIG. 1 is a graph showing the change of the L value of the coating color with heating time after heating steel plates having different precoat thicknesses;
FIG. 2 is a graph showing the change of the values of a and b of 5 μm coating color of a precoat layer with heating time;
FIG. 3 is a graph showing the change of the values of a and b of a 19 μm coating color of a precoat layer with heating time;
FIG. 4 is a graph showing the change of the values of a and b of a coating color of 33 μm of a precoat layer with heating time;
FIG. 5 is a graph showing the degree of alloying of a precoated coating layer with a thickness of 3 μm or more and 19 μm or less, as judged by the values of the coating colors L, a and b after heating;
FIG. 6 is a graph showing the degree of alloying of a precoated coating layer with a thickness of greater than 19 μm and less than or equal to 33 μm as judged by the values of the coating colors L, a and b after heating;
FIG. 7 is a diagram of a suitable alloying window for a pre-coat coating thickness of 3 μm or more and 19 μm or less;
FIG. 8 is a diagram of a suitable alloying window for a pre-coat coating thickness greater than 19 μm and less than or equal to 33 μm;
FIG. 9 is a view showing the structure of a coating layer before heating a steel sheet having a precoating thickness of 5 μm (a), 19 μm (b) and 33 μm (c), respectively;
FIG. 10 is a diagram of the structure of a coating with under-alloyed (a), properly alloyed (b), and over-alloyed (c) coating with alloying degree;
FIG. 11 is a graph showing the peeling of the coating after the welding of the coating in example 14;
FIG. 12 is a graph showing the peeling of the coating after the welding of the coating in example 15.
Detailed Description
The present invention will be described in detail with reference to examples. The following examples or experimental data are intended to illustrate the present invention, and it should be apparent to those skilled in the art that the present invention is not limited to these examples or experimental data.
Firstly, the thickness of the steel plate with the pre-coating aluminum or aluminum alloy coating is 0.4-3.0 mm, wherein the thickness of the pre-coating is 3-33 mu m, the thickness of the steel plate is 1.0mm, 1.4mm and 2.0mm respectively, the thickness of the pre-coating is 5 mu m, 19 mu m and 33 mu m respectively, and the pre-coating is coated on the upper surface and the lower surface of the steel plate.
Wherein, the base steel of the steel plate adopts 22MnB5 commonly used in the market, the precoating coating of the invention can be realized by hot dip plating, the typical hot dip plating solution comprises (by mass percent) 8-11% Si, 2-4% Fe and the balance of aluminum or aluminum alloy and unavoidable impurities, however, the invention is not limited to the coating mode and the plating solution composition, and other coating modes or other aluminum or aluminum alloy compositions can be adopted. The method is characterized in that Si is added into the plating solution, mainly in the hot dip plating process, an Fe-Al-Si inhibition layer is formed on the surface of the steel plate, so that the formation of brittle phases Fe 2Al5 can be effectively prevented, the forming capacity of the coating is improved, but when the Si content is too high, the surface quality of the steel plate is affected, and experimental researches show that the Si content in the aluminum liquid is generally controlled to be 8-11% more suitable. The solubility of Fe is different at different plating solution temperatures, the temperature of the conventional aluminum silicon plating solution is 640-680 ℃, and the solubility of Fe in the plating solution is 2-4%.
As an example, the base steel and the precoat according to the invention have the compositions shown in table 1.
TABLE 1 base Steel of the invention and precoating composition
Wherein bal represents the balance, among other elements.
The pre-coated aluminum or aluminum alloy coated steel plate can be manufactured by the following technical processes: molten iron pretreatment, converter smelting, alloy fine adjustment, refining, continuous casting, hot rolling, pickling cold rolling and hot dip plating.
(1) And (3) molten iron pretreatment: firstly, before molten iron is added into a steelmaking furnace, pretreatment for removing impurity elements or recovering valuable elements is required, and slag skimming is generally required for the pretreatment.
(2) Smelting in a converter: molten iron, scrap steel, ferroalloy, etc. are smelted into molten steel in a converter, and deoxidization alloying is generally required at the time of tapping.
(3) Alloy fine tuning: and further finely adjusting the content of alloy elements of molten steel after converter smelting.
(4) Refining: molten steel is refined by adopting RH, LF and other modes, and is generally injected into a refining ladle to perform procedures of argon blowing, degassing, ladle refining and the like, so that purer steel is obtained.
(5) Continuous casting: pouring the refined molten steel into a tundish, distributing the molten steel into each crystallizer by the tundish, forming and crystallizing the castings, and then pulling out the castings and cutting the castings into slabs with certain lengths.
(6) And (3) hot rolling: and (3) hot rolling the slab at 1000-1300 ℃, controlling the hot rolling tapping temperature to be above 1100 ℃, and controlling the final rolling temperature to be above 600 ℃ to obtain the hot rolled steel plate. And coiling the hot rolled steel plate, wherein the coiling temperature is controlled below 800 ℃.
(7) Acid pickling cold rolling: and further carrying out pickling cold rolling on the hot-rolled steel plate to obtain a pickling cold-rolled steel plate.
(8) Hot dip plating: the production flow of the hot dip plating process is as follows: substrate cleaning, continuous annealing, dip plating, coating thickness control, and cooling after plating.
(A) Cleaning a substrate: in order to ensure good coating quality, the single-sided residual oil quantity of the steel plate after cleaning is controlled below 20mg/m 2, and the single-sided residual iron is controlled below 10mg/m 2;
(b) Continuous annealing: the annealing temperature and atmosphere are critical to the quality of the hot dip coating and the structure and performance of the product, the annealing temperature is controlled at 720-850 ℃, the annealing heat preservation time is controlled at 60-120 s, the reducing section atmosphere is adopted, the H 2+N2 (according to volume percent) is 5-10%, the oxygen content is controlled below 20ppm, and the dew point is controlled at-60-0 ℃;
(c) And (3) dip plating: the immersion plating temperature is controlled to be 640-680 ℃ and the immersion plating time is 2-8 s;
(d) Coating thickness control: the thickness of the coating is controlled by blowing nitrogen or compressed air through an air knife, and the thickness of the coating is controlled to be 3-33 mu m on one side;
(e) Cooling after plating: cooling after plating by air cooling, cooling the steel plate to below 300 ℃, and then cooling the steel plate to below 100 ℃. And (5) continuing to perform finishing, oiling, trimming, coiling and other operations, and finally, discharging the coiled material.
The 5 μm, 19 μm, 33 μm precoat structures produced by the above procedure are shown in FIG. 9.
According to analysis, the matrix structure of each steel plate is a ferrite structure and a pearlite structure, and the precoating layer is an intermetallic compound layer (Fe 2Al5、Fe2SiAl7) and an aluminum coating layer respectively from the side of the matrix to the surface. The thickness of the intermetallic compound layer of each precoat layer was equal to about 4.5 μm (Fe 2Al5 layer thickness 0.5 μm or less), and the difference was in the thickness of the aluminum coating layer, which was 0.5 μm, 14.5 μm, 28.5 μm, respectively.
Next, three suitable heating processes were selected for each of the above-mentioned base plates having thicknesses of 1mm, 1.4mm, and 2.0mm, and precoated layers having thicknesses of 5 μm, 19 μm, and 33 μm, respectively, to heat the base plates, and a total of 27 examples were taken, and after heating, the coating color was detected (invention), and as a comparison, the coating structure and coating composition were also detected (comparison). The color detection equipment adopts a HunterLab XE color difference meter, and the coating structure and coating composition detection equipment adopts a scanning electron microscope and an energy spectrum analyzer. It should be noted that, in order to avoid detection analysis errors caused by uneven color of the coating, a part with a relatively uniform color needs to be selected for color detection.
General procedure for color detection: cutting a plate or a part into a proper size, detecting, and detecting a coating structure and a coating composition in a general process: cutting plate materials or parts into proper sizes, processing metallographic samples, preparing metallographic analysis samples and detecting. The time required by the color detection is less than 5min (the invention) through statistics, and the invention has simple and convenient operation and lower technical requirements for operators. The time required for detecting the coating structure and the coating components is more than 30min, the operation is complex, and the technical requirements and the proficiency requirements on operators are high. By contrast, the invention judges the alloying degree of the coating through color detection, and has simpler and more convenient operation and higher efficiency than the judgment of the alloying degree of the coating through the coating structure and the coating composition.
Table 2 shows the coating color (invention), coating structure and coating composition (comparative) and the corresponding coating alloying degree judgment for examples 1 to 27.
TABLE 2 color detection of coating after heating of precoated Steel sheet (invention), coating Structure and coating composition detection (comparative)
The inventors have found that when the coating is underalloyed, there may be an incompletely transformed aluminum coating or Fe 2SiAl7 on the outermost surface of the coating after heating; when the coating is properly alloyed, the coating structure of the pre-coating thin coating (the thickness of the coating is more than or equal to 3 mu m and less than or equal to 19 mu m) is a diffusion layer (Fe and Fe 3 Al), a FeAl layer, a Fe-Al-Si layer and a continuous or discontinuous surface layer sequentially from the substrate to the surface, and the coating structure of the pre-coating thick coating (the thickness of the coating is more than or equal to 19 mu m and less than or equal to 33 mu m) is a diffusion layer (Fe and Fe 3 Al), a FeAl layer, a Fe-Al-Si layer and a FeAl layer sequentially from the substrate to the surface; when the coating is overalloyed, the coating structure of the pre-coated thin coating is generally composed of a diffusion layer, a Fe-Al layer and a Fe-Al-Si layer, or a diffusion layer, a Fe-Al-Si layer and a discontinuous surface layer, or a diffusion layer and a Fe-Al-Si layer, or only a diffusion layer from the substrate to the surface; wherein the discontinuous surface layer is a mixed structure of Fe-Al and Fe-Al-Si, and the diffusion layer is Fe and Fe 3 Al. The pre-coated thick coating layer structure is still a four-layer structure, and a diffusion layer (Fe and Fe 3 Al), a FeAl layer, a Fe-Al-Si layer and a FeAl layer are sequentially arranged from the substrate to the surface, and at this time, one remarkable characteristic of the appearance of the coating layer is that the number and the size of holes in the coating layer are rapidly increased.
Examples 13, 14, 15 are pre-coat thicknesses of 19 μm, and after heating the coatings were under-alloyed, suitably alloyed and over-alloyed, respectively, the coating structure and composition of which are shown in fig. 10. When the coating is under-alloyed, the coating is of a five-layer structure, the side to the surface of the substrate are respectively a Fe 2Al5、Fe2SiAl2、Fe2Al5、Fe2SiAl7 layer and an aluminum layer, and the outermost layer contains unconverted Fe 2SiAl7 and an aluminum coating; when the coating is properly alloyed, the coating structure is a four-layer structure, and a diffusion layer and Fe 2Al5、Fe5SiAl5、Fe2Al5 are respectively arranged from the side of the substrate to the surface; when the coating is in a super-alloyed structure, the coating is in a two-layer structure, a diffusion layer and FeAl (the Si content is below 4%) are respectively arranged from the side to the surface of the substrate, the number of holes in the coating is large, and the holes are positioned at the interface of the diffusion layer and the FeAl layer. The number of holes in the under-alloyed or suitably alloyed coating is significantly lower than in the over-alloyed coating.
More importantly, when the welding performance tests of examples 14, 15 were performed, the weldability welding current range of example 15 was found to be significantly lower than that of example 14, and the results are shown in table 3.
TABLE 3 welding performance results (GWS-5A standard)
In addition, it was found that the coating peeling degree difference between the electrode tip contact coating after welding of examples 14 and 15 was large, but the coating peeling of example 14 was not obvious, but the coating peeling of example 15 was serious, the peeling part was an Fe-Al layer, the peeling position was located around the hole, and the peeling of the coating was shown in FIGS. 11 and 12, respectively. Therefore, it is considered that when the number of holes in the coating is large and the size is large, the coating is liable to peel around the holes, and the peeled coating adheres to the welding electrode, so that the electrode wear is aggravated and the welding performance is worsened. In addition, the number of holes in the coating is large, the coating is seriously stripped after stamping forming, and the corrosion resistance of the coating is reduced, the mold is polluted and the like.
When the degree of alloying of the coating was judged by the coating structure and the coating composition, the presence of unconverted Fe 2SiAl7 or aluminum coating on the outermost surface of the coating after heating in examples 1, 4, 7, 10, 13, 16, 19, 22, 25 was judged to be under-alloyed. When the color detection judges the alloying degree of the coating, the L value in the examples 1, 4, 7, 13 and 22 is more than 42, and the underalloying of the coating can be judged; the total thickness of the steel plate in the embodiment 10 is 1.4mm, the thickness of the precoat layer is 5 mu m, 35 < L < 42, a is less than or equal to 1 and b is less than or equal to 1, the coating layer can be underalloyed or overalloyed, the alloying degree can be judged according to the graph ABCD, the heating temperature is 930 ℃ in the process window in the embodiment 10, but the heating time is 110s lower than the process window, and the coating layer can be judged to be underalloyed; the total thickness of the steel plate in the example 16 is 1.4mm, the thickness of the precoat layer is 33 mu m, L is less than or equal to 35 and a is more than 1 in the example 16, and the coating layer can be judged to be under-alloyed; the total thickness of the steel plate in the embodiment 19 is 2.0mm, the thickness of the precoat layer is 5 mu m, L is less than or equal to 35, a is less than or equal to 1, b is less than or equal to 1, the coating layer can be under-alloyed or properly alloyed, the alloying degree can be judged according to the pattern EFGH, the heating time 240s is in the process window in the embodiment 19, but the heating temperature 860 ℃ is lower than the process window, and the coating layer can be judged to be under-alloyed; the total thickness of the steel sheet of example 25 was 2.0mm, the thickness of the pre-coating layer was 33 μm, 35 < L < 42 and a >1 and b >1, the coating layer could be under-alloyed or over-alloyed, the degree of alloying could be judged according to the pattern MNOP, the heating temperature of 940℃was within the process window in example 25, but the heating time 120s was lower than the process window, and the coating layer could be judged as under-alloyed.
Examples 2, 5, 8, 11, 14, 17, 20, 23, 26 were all suitable alloying when judging the degree of alloying of the coating by the coating structure, the coating composition, wherein 2, 5, 11, 14, 20, 23 were the precoated thin coating, the coating structure was the diffusion layer, the Fe 2Al5, the Fe-Al-Si intermetallic compound layer and the continuous or discontinuous surface layer from the substrate side to the surface, the coating structure was the precoated thick coating, and the coating structure was the diffusion layer, the Fe 2Al5, the Fe-Al-Si layer and the surface layer (Fe 2Al5) from the substrate side to the surface, respectively. When the degree of alloying of the coating is judged by color detection, examples 2, 5, 11, 14, 20 and 23 are precoated thin coatings, in the examples, L is less than or equal to 35, a is less than or equal to 1.0 and b is less than or equal to 1.0, the coating can be properly alloyed or underalloyed, the degree of alloying can be judged according to the patterns ABCD and EFGH, the heating temperature and the heating time are both within a process window, and the coating can be judged to be properly alloyed; examples 8, 17, 26 are pre-coated thick coatings where L < 42 and a.ltoreq.1 and b.ltoreq.1, the coatings were judged to be properly alloyed.
When the alloying degree of the coating is judged by the coating structure and the coating composition, all of the examples 3, 6, 9, 12, 15, 18, 21, 24 and 27 are overalloyed, wherein the examples 3, 6, 12, 15, 21 and 24 are precoated thin coatings, the coating structure is respectively a diffusion layer and FeAl from the side to the surface of the substrate, the examples 9, 18 and 27 are precoated thick coatings, the coating structure is respectively a diffusion layer, a Fe 2Al5, a Fe-Al-Si layer and a surface layer (Fe 2Al5) from the side to the surface of the substrate, and at the moment, more holes with larger sizes are formed in the coating, and the number of the holes with the size of more than 0.5 micrometer in each 1000 mu m 2 is not less than 10. When the color detection judges the alloying degree of the coating, examples 3, 6, 15, 21 and 24 are precoated thin coatings, and L is smaller than 42 and a is larger than 1 or b is larger than 1, the coating can be judged to be overalloyed; the total thickness of the steel plate in the embodiment 12 is 1.4mm, the thickness of the precoat layer is 5 mu m, 35 < L < 42 and a is less than or equal to 1 and b is less than or equal to 1, the coating layer can be underalloyed or overalloyed, the alloying degree can be judged according to the graph ABCD, the heating temperature in the embodiment 12 is 930 ℃ in a process window, but the heating time is 400s higher than the process window, and the coating layer can be judged to be overalloyed; examples 9, 18, 27 are pre-coated thick coatings, where 35 < L < 42 and a > 1 or b > 1, where the coating may be under-alloyed or over-alloyed, where the degree of alloying may be determined based on the pattern IJKL and the pattern MNOP, and examples 9, 18, 27 have heating times of 300s, 340s, 360s, respectively, within the process window, but a heating temperature of 1000 ℃ above the process window may determine that the coating is over-alloyed.
Through the embodiment, the coating alloying degree is judged through the coating color detection and alloying process window after heating and is consistent with the coating alloying degree through the coating structure and the composition, and compared with the coating alloying degree (compared) judged through the coating structure and the coating composition, the coating alloying degree is judged through the color detection and alloying process window (the invention) more conveniently and more efficiently.
The foregoing detailed description of a method for rapidly determining the degree of alloying of an aluminum or aluminum alloy coating with reference to the examples is illustrative and not limiting, and several examples can be enumerated in the limited scope, and therefore variations and modifications within the generic and specific scope of the invention should be considered within the scope of the invention.
Claims (7)
1. A method for rapidly judging the alloying degree of an aluminum or aluminum alloy coating is characterized in that the alloying degree of the coating is judged by combining the values of L, a and b in the color space of Hunter L, a and b of the coating and an alloying window;
when L is more than or equal to 42, the coating is underalloyed;
When the thickness of the precoating coating is more than or equal to 3 mu m and less than or equal to 19 mu m, when L is less than or equal to 35 and a is less than or equal to 1 and b is less than or equal to 1, the coating is suitable alloyed or underalloyed; when L is more than 35 and less than 42, a is less than or equal to 1, b is less than or equal to 1, and the coating is under-alloyed or over-alloyed; when L < 42 and a > 1 or b > 1, the coating is overalloyed;
When the thickness of the pre-coating is more than 19 mu m and less than or equal to 33 mu m, when L is less than or equal to 35 and a is more than 1 or b is more than 1, the coating is under-alloyed; when L is less than 42 and a is less than or equal to 1 and b is less than or equal to 1, the coating is properly alloyed; when 35 < L < 42 and a > 1 or b > 1, the coating is under-alloyed or over-alloyed;
Judging the alloying degree of the coating according to an alloying window when the thickness of the precoating coating is more than or equal to 3 mu m and less than or equal to 19 mu m, L is less than or equal to 35 and a is less than or equal to 1 and b is less than or equal to 1 and when L is more than 35 and less than 42 and a is less than or equal to 1 and b is less than or equal to 1;
if the heating temperature or heating time of the alloying is lower than the heating temperature or heating time defined by the alloying process window, the coating is under-alloyed;
If the heating temperature and heating time of the alloying are both within the alloying process window, the coating is suitably alloyed;
If the heating temperature or heating time of the alloying is higher than the heating temperature or heating time defined by the alloying process window, the coating is over-alloyed;
When the thickness of the precoating coating is more than 19 mu m and less than or equal to 33 mu m, and when 35 < L < 42 and a is more than 1 or b is more than 1, the method for judging the coating to be under-alloyed or over-alloyed is as follows: the coating is under-alloyed if the heating temperature or heating time of the alloying is lower than the heating temperature or heating time defined by the alloying process window, and the coating is over-alloyed if the heating temperature or heating time of the alloying is higher than the heating temperature or heating time defined by the alloying process window.
2. The method for rapidly determining the degree of alloying of an aluminum or aluminum alloy coating according to claim 1, wherein the coating is formed by interdiffusion of a precoated aluminum or aluminum alloy coated steel sheet with a base steel after heating.
3. The method for rapidly determining the alloying degree of an aluminum or aluminum alloy coating according to claim 1 or 2, wherein the plating solution for forming the coating comprises the following components in percentage by weight: 8-11% of Si, 2-4% of Fe and the balance of aluminum and unavoidable impurities.
4. The method for rapidly judging the alloying degree of an aluminum or aluminum alloy coating according to claim 1 or 2, wherein when the alloying degree of the coating is proper alloying, when the thickness of the precoating coating is more than or equal to 3 μm and less than or equal to 19 μm, the coating structure sequentially comprises a diffusion layer, a Fe-Al-Si layer and a continuous or discontinuous surface layer from the substrate to the surface, wherein the continuous surface layer is the Fe-Al layer, and the discontinuous surface layer is a mixed structure of Fe-Al and Fe-Al-Si;
When the alloying degree of the coating is proper alloying, the thickness of the precoated coating is more than 19 mu m and less than or equal to 33 mu m, and the coating structure sequentially comprises a diffusion layer, a Fe-Al-Si layer and a Fe-Al layer from the substrate to the surface.
5. The method for rapidly determining the alloying degree of an aluminum or aluminum alloy coating according to claim 1 or 2, wherein when the alloying degree of the coating is under-alloying, an aluminum layer or Fe 2SiAl7 is present on the surface of the coating.
6. The method for rapidly judging the alloying degree of an aluminum or aluminum alloy coating according to claim 1 or 2, wherein when the alloying degree of the coating is overalloying and the thickness of the precoating coating is not less than 3 μm and not more than 19 μm, the coating structure is composed of a diffusion layer, an Fe-Al layer, and an Fe-Al-Si layer, or a diffusion layer, an Fe-Al-Si layer, and a discontinuous surface layer, or a diffusion layer and an Fe-Al-Si layer, or a diffusion layer alone, in this order from the substrate to the surface; wherein the discontinuous surface layer is a mixed structure of Fe-Al and Fe-Al-Si;
when the alloying degree of the coating is overalloying, the thickness of the precoated coating is more than 19 mu m and less than or equal to 33 mu m, and the coating structure sequentially comprises a diffusion layer, a Fe-Al-Si layer and a Fe-Al layer from the substrate to the surface.
7. The method for rapidly determining the degree of alloying of an aluminum or aluminum alloy coating according to claim 1 or 2, wherein the degree of alloying of the coating is not less than 10 holes per 1000 μm 2 of the coating of more than 0.5 μm.
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