CN115058630A - A kind of aluminum-zinc-magnesium coated steel plate and preparation method thereof - Google Patents

Abstract

The invention particularly relates to an aluminum-zinc-magnesium coated steel sheet and a preparation method thereof, belonging to the technical field of coating. An aluminum-zinc-magnesium-coated steel sheet, comprising a substrate and a coating on the surface of the substrate, and the chemical composition of the coating includes in mass percentage; Al: 47-58%, Mg: 2-3%, Si: 1.5-2.5%, Ni : 0.05‑0.80%, the balance being Zn and inevitable impurities. It can effectively improve the surface quality of the Al-Zn-Mg plated steel sheet by adding Al, Mg, Si and Ni elements in the coating layer and reasonably adjusting the mass percentage range of each element.

Description

A kind of aluminum-zinc-magnesium coated steel plate and preparation method thereof

technical field

The invention belongs to the technical field of coating, and particularly relates to an aluminum-zinc-magnesium-coated steel sheet and a preparation method thereof.

Background technique

Al-Zn-Mg coated steel sheet is a new type of high corrosion-resistant alloy coated steel sheet. This coating is developed on the basis of traditional aluminum-zinc coating. Magnesium is added to the coating, which significantly improves the flat corrosion resistance and incision corrosion resistance of the coating. It can be widely used in the manufacture of building exterior walls. However, the exterior wall of the building has higher requirements on the surface appearance quality of the coating.

The surface of Al-Zn-Mg coating usually contains coarse Al dendrite grains. If the size of such dendrite grains exceeds 2mm, there will be visible surface color differences and color changes during use. If it exceeds 5mm, it will appear. The feel is bumpy. Therefore, it is required that the surface grain size of the aluminum-zinc-magnesium coating should be less than 2mm as much as possible, preferably less than 1mm. However, the surface grain size of the traditional Al-Zn coating is difficult to be less than 1mm.

SUMMARY OF THE INVENTION

The purpose of this application is to provide an aluminum-zinc-magnesium-coated steel sheet and a preparation method thereof, so as to solve the technical problem of poor surface quality of the aluminum-zinc-magnesium coated steel sheet in the prior art.

The embodiment of the present invention provides an aluminum-zinc-magnesium-coated steel sheet, which includes a substrate and a coating on the surface of the substrate, and the chemical composition of the coating includes in mass percentage;

Al: 47-58%, Mg: 2-3%, Si: 1.5-2.5%, Ni: 0.05-0.80%, and the balance is Zn and inevitable impurities.

Optionally, an alloy layer is formed between the substrate and the plating layer, and the thickness of the alloy layer is 0.2-2 μm.

Optionally, the mass percentage of Si in the alloy layer is greater than or equal to 10%.

Optionally, there is oxide in the surface layer of the substrate, and the volume percentage of the oxide is 0.1-5%; wherein: the thickness of the surface layer is 1 μm.

Based on the same inventive concept, the embodiment of the present invention also provides a preparation method of the above-mentioned Al-Zn-Mg coated steel sheet, comprising the following steps:

obtaining a slab of the substrate;

subjecting the slab to heating, rough rolling, finishing rolling, coiling, first cooling, cold rolling and continuous annealing to obtain an annealed substrate;

subjecting the annealed substrate to hot dip plating, second cooling and finishing to obtain the aluminum-zinc-magnesium-coated steel sheet;

in:

The chemical composition of the hot dip plating solution is the same as the chemical composition of the plating layer.

Optionally, the temperature of the coiling is 680-730°C.

Optionally, the rate of the first cooling is less than or equal to 1°C/s.

Optionally, the temperature of the continuous annealing is 750-850°C, and the dew point temperature of the continuous annealing is -10-10°C.

Optionally, the temperature of the bath of the hot dip plating is 530-580° C., and the time of the hot dip plating is less than or equal to 60s.

Optionally, the second cooling includes cooling to 450° C. at a preset cooling rate, and the preset cooling rate is greater than or equal to 10° C./s.

One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

The aluminum-zinc-magnesium-coated steel sheet provided by the embodiment of the present invention effectively improves the surface quality of the aluminum-zinc-magnesium-coated steel sheet by adding Al, Mg, Si, and Ni elements to the coating layer and reasonably adjusting the mass percentage range of each element. Specifically, by adding Al element and controlling its content, the cracking of the coating caused by the bending of the coating is dealt with, and the surface quality of the coating is initially improved; by adding Mg and Si, a Mg-Si compound is formed to refine the Al dendrite and further improve the surface of the coating Quality; by adding Ni, it reacts with the Mg-Si compound to form a Mg-Si-Ni compound with a higher precipitation temperature, and its precipitation temperature is close to the solidification temperature of the Al dendrite, thereby ensuring that the Mg-Si-Ni compound solidifies in the Al dendrite Precipitation before or during solidification, further refines Al dendrites, and further improves the surface quality of the coating; and Ni can also form Fe-Al-Ni compounds, which can inhibit the growth rate of the alloy layer formed between the coating and the substrate, and then Inhibiting the rapid growth of the alloy layer will lead to the phenomenon of uneven surface, thereby further improving the flatness of the surface of the coating, that is, improving the surface quality of the coating.

The above description is only an overview of the technical solutions of the present invention, in order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the description, and in order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand , the following specific embodiments of the present invention are given.

Description of drawings

In order to illustrate the technical solutions in the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

FIG. 1 is a flowchart of a method provided by an embodiment of the present invention.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly presented therefrom. It should be understood by those skilled in the art that these specific embodiments and examples are used to illustrate the present invention, but not to limit the present invention.

Throughout the specification, unless specifically stated otherwise, terms used herein are to be understood as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification takes precedence. The technical terms used herein are only for the purpose of describing specific embodiments, and are not intended to limit the protection scope of the present invention. For example, room temperature may refer to a temperature in the range of 10 to 35°C.

Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or can be prepared by existing methods.

The technical solutions of the embodiments of the present application are to solve the above-mentioned technical problems, and the general idea is as follows:

According to a typical embodiment of the present invention, an aluminum-zinc-magnesium-coated steel sheet is provided, comprising a substrate and a coating on the surface of the substrate, and the chemical composition of the coating includes in mass percentage;

Al: 47-58%, Mg: 2-3%, Si: 1.5-2.5%, Ni: 0.05-0.80%, and the balance is Zn and inevitable impurities.

The aluminum-zinc-magnesium-coated steel sheet provided by the embodiment of the present invention effectively improves the surface quality of the aluminum-zinc-magnesium-coated steel sheet by adding Al, Mg, Si, and Ni elements to the coating layer and reasonably adjusting the mass percentage range of each element. Specifically, by adding Al element and controlling its content, the cracking of the coating caused by the bending of the coating is dealt with, and the surface quality of the coating is initially improved; by adding Mg and Si, a Mg-Si compound is formed to refine the Al dendrite and further improve the surface of the coating Quality; by adding Ni, it reacts with the Mg-Si compound to form a Mg-Si-Ni compound with a higher precipitation temperature, and its precipitation temperature is close to the solidification temperature of the Al dendrite, thereby ensuring that the Mg-Si-Ni compound solidifies in the Al dendrite Precipitation before or during solidification, further refines Al dendrites, and further improves the surface quality of the coating; and Ni can also form Fe-Al-Ni compounds, which can inhibit the growth rate of the alloy layer formed between the coating and the substrate, and then Inhibiting the rapid growth of the alloy layer will lead to the phenomenon of uneven surface, thereby further improving the flatness of the surface of the coating, that is, improving the surface quality of the coating.

The above-mentioned main chemical elements and limited ranges are described in detail as follows:

Al: The Al element in the Al-Zn-Mg coating can provide the coating with high-quality corrosion resistance, and the Al element content should not be less than 47%. However, if the content of aluminum element exceeds 58%, the coating will be prone to cracking during the bending process, which will lead to the reduction of the corrosion resistance of the coating.

Mg: Adding 2% Mg element can significantly improve the corrosion resistance of the coating. The mechanism is that Mg in the coating will preferentially dissolve into the water film on the surface of the coating in the atmospheric environment, and react with dissolved carbon dioxide in the water film. A dense protective film is precipitated, which can exist stably in neutral and weak alkaline environments, and can also change the electrolyte solution on the surface of the coating to a weak alkaline solution, thereby improving the corrosion resistance of the coating. At the same time, the Mg element in the coating can also react with the added Si element to form a small amount of Mg-Si compound, which can have a certain effect of refining Al dendrites. Therefore, the content of Mg element in the coating cannot be too low, and needs to reach 2%. However, if the content of Mg element is too high, a large amount of Mg-Zn compounds and Mg-Si compounds will appear in the coating. These two compounds have a great influence on the bending properties of the coating, resulting in cracks during the bending process of the coating and reducing the coating. Corrosion resistance and appearance quality. Therefore, the Mg content in the coating does not exceed 3%.

Si: Si can react with the Fe-Al alloy, occupy the vacancies of the Fe-Al alloy, and also block the diffusion of Fe through the Fe-Al alloy layer. Therefore, the thickness of the alloy layer can be reduced, and the surface structure of the coating layer can be optimized. However, if too much Si is added, more Mg-Si compounds and Mg-Si-Ni compounds will be formed in the alloy layer. There is an incompatibility problem between this compound and the Fe-Al compound because the lattice sizes of the two compounds are quite different. This will cause internal stress in the coating alloy layer, resulting in loosening of the alloy layer itself and worsening the bending adhesion of the coating. Therefore, the Si element content in the coating cannot exceed 2.5%. In addition, adding too much Si will cause the alloy layer to be too thin, and will also affect the bending adhesion of the coating and the steel plate. Since Mg is added to the coating, it will absorb a part of the Si element to form a Mg-Si compound. Therefore, the content of Si in the coating is higher than that of the traditional Al-Zn coating, and should not be lower than 1.5%, preferably not lower than 2.0%. .

Ni: In order to further increase the precipitation temperature of Mg-Si, a certain amount of nickel is added to the plating layer. Nickel element can react with Mg-Si compound to form Mg-Si-Ni compound, and the precipitation temperature of this compound is higher than that of Mg-Si compound. Adding 0.05% Ni to the coating layer can make the precipitation temperature of Mg-Si-Ni about 20°C higher than that of Mg-Si compound. However, if 0.8% Ni is added, the precipitation temperature is increased by 80 °C, and the precipitation temperature is close to the solidification temperature of aluminum dendrites. If the Ni element continues to be added, more Al-Ni alloy phases and Mg-Ni alloy phases will appear in the coating. These two alloy phases are distributed in needle shape, which easily lead to cracks after bending of the coating. Therefore, the content of Ni element in the coating is in the range of 0.05%-0.8%.

The addition of Ni element to the coating layer has another effect, that is, Fe-Al-Ni compound can be formed in the alloy layer of the coating layer, which can inhibit the rapid growth of the alloy layer and make the thickness of the alloy layer thinner. The alloy layer is usually an Fe-Al compound. This compound alloy layer provides the basic coating adhesion to the coating. However, the Fe-Al phase will grow rapidly at a higher hot-dip plating temperature, resulting in an uneven structure on the surface of the alloy layer. This uneven structure will cause significant local differences in the growth rate of aluminum dendrites. As a result, local aluminum dendrites grow too fast, forming coarse crystals and deteriorating the surface quality of the coating. The Fe-Al phase is a substance with a relatively loose spatial structure, which contains a large number of vacancies, which makes it easy for Fe to diffuse out through the Fe-Al alloy layer and continue to react with Al in the plating solution, making the Fe-Al alloy. The layers keep growing. After adding Ni, Ni can occupy the center of the Fe-Al alloy layer to form a Fe-Al-Ni alloy layer, which reduces the diffusion ability of Fe in the alloy, slows down the growth rate of the alloy layer, and forms a thin and uniform alloy layer. However, adding too much Ni will cause the alloy layer to be too thin and deteriorate the bending adhesion between the coating and the steel plate.

Preferably, an alloy layer is formed between the substrate and the plating layer, and the thickness of the alloy layer is 0.2-2 μm.

As an optional embodiment, the mass percentage of Si in the alloy layer is greater than or equal to 10%.

As an optional embodiment, the surface layer of the substrate has oxides, and the volume percentage of the oxides is 0.1-5%; wherein: the thickness of the surface layer is 1 μm.

The mechanism for controlling the above parameter ranges is that in order to further suppress the diffusion of Fe element in the steel sheet to form an uneven alloy layer, a large amount of oxides are also formed in the superficial layer of the steel sheet. The formation of oxides can effectively inhibit the external diffusion of Fe elements, thereby reducing the rapid growth of the alloy layer. In order to achieve this purpose, the volume fraction of oxide must reach 0.1%, and at the same time, it should be distributed in the range of 1 micron below the surface, otherwise it will not be able to achieve the purpose of hindering. However, if the volume fraction of oxides is too large, abnormal wrinkles will appear on the surface of the steel sheet during bending, resulting in cracking of the coating, so the volume fraction does not exceed 5%.

According to another typical embodiment of the present invention, there is provided a manufacturing method of the aluminum-zinc-magnesium-coated steel sheet provided above, comprising the following steps:

S1. Obtain the slab of the substrate.

S2. The slab is subjected to heating, rough rolling, finishing rolling, coiling, first cooling, cold rolling and continuous annealing to obtain an annealed substrate.

S3, subjecting the annealed substrate to hot dip plating, second cooling and smoothing to obtain the aluminum-zinc-magnesium-coated steel sheet.

Wherein: the chemical composition of the hot-dip plating bath is the same as the chemical composition of the plating layer.

As an optional embodiment, the temperature of the coiling is 680-730°C.

As an optional embodiment, the rate of the first cooling is less than or equal to 1°C/s.

The reason for controlling the coiling temperature and the first cooling rate is that in the process of the first cooling, the oxygen in the air can react with the hot-rolled coil formed by hot rolling, and a relatively slow cooling rate and a relatively high coiling rate are used. The temperature is conducive to the penetration of oxygen into the steel matrix and the formation of oxides inside the superficial layer of the hot rolled coil. However, the coiling temperature is too high, which will lead to the rapid formation of a dense iron oxide layer on the surface, which hinders the infiltration of oxygen. Therefore, the specified coiling temperature range is 680-730 °C, and the first cooling rate after coiling does not exceed 1 °C/ s.

As an optional embodiment, the temperature of the continuous annealing is 750-850°C, and the dew point temperature of the continuous annealing is -10-10°C.

The reason for controlling the above parameters is that in the process of continuous annealing, internal oxides can also be formed by oxidation. Generally speaking, the time of continuous annealing is relatively short, so higher temperature is required to form enough oxides, but continuous annealing is required. The annealing temperature should not be too high, otherwise it will easily lead to the formation of excessive oxides in the superficial layer. The dew point temperature of the atmosphere in the annealing process represents the oxygen content in the atmosphere. The higher the dew point temperature, the more oxygen in the atmosphere. If the dew point temperature is relatively low, the Si and Mn alloy elements in the steel plate will be oxidized on the surface, and a shallow surface layer cannot be formed. The internal oxides, if the dew point temperature is too high, will lead to the formation of iron oxide, which cannot form oxides in the inner shallow surface layer. Only when the dew point temperature is between -10°C and 10°C, can a large amount of iron oxide be formed inside the shallow surface layer of the steel plate. oxide particles.

As an optional embodiment, the temperature of the hot dip plating solution is 530-580° C., and the time of the hot dip plating is less than or equal to 60s.

The reason for controlling the above parameter range is: in order to achieve the effect of refining aluminum dendrites, it is necessary to ensure that the Mg-Si compound is precipitated before or during the solidification of aluminum dendrites, and at the same time, it cannot be too coarse. The temperature during plating should not be too high, and the second cooling rate should be fast enough, so that the Mg-Si compound can be precipitated before the aluminum dendrites are completely solidified. Therefore, control the temperature range of hot dip plating to be 530℃ to 580℃. If the temperature is too high, the aluminum dendrites will completely solidify and grow, forming coarse grains. After the coating is bent, the surface is cracked, which affects the appearance quality and the corrosion resistance of the coating.

The time of hot dip coating affects the growth process of the alloy layer. In higher temperature baths, the longer the hot dip plating time, the more pronounced the growth of the alloy layer will be. Therefore, it is stipulated that the time of hot-dip plating should not exceed 60 seconds.

As an optional embodiment, the second cooling includes cooling to 450° C. at a preset cooling rate, and the preset cooling rate is ≥10° C./s.

The reason for controlling the above parameters is that combined with the control of the hot-dip plating temperature, and further controlling the rate of the first half of the second cooling, it can effectively ensure that Mg-Si can be precipitated before the solidification of aluminum dendrites.

The present application will be described in detail below with reference to the examples, comparative examples and experimental data.

Examples 1-7

An aluminum-zinc-magnesium-coated steel sheet is provided, including a substrate and a coating on the surface of the substrate. The parameters are shown in Table 1.

Table 1 Parameters of the aluminum-zinc-magnesium-coated steel sheets of Examples 1-7

The preparation method of the above-mentioned aluminum-zinc-magnesium coated steel sheet, comprises the following steps:

S1. Obtain the slab of the substrate.

S2. The slab is subjected to heating, rough rolling, finishing rolling, coiling, first cooling, cold rolling and continuous annealing to obtain an annealed substrate.

S3, subjecting the annealed substrate to hot dip plating, second cooling and smoothing to obtain the aluminum-zinc-magnesium-coated steel sheet.

The parameters of the preparation method of each embodiment are shown in Table 2 respectively.

The parameters of the preparation method of table 2 embodiment 1-7

Comparative Examples 1-5

An aluminum-zinc-magnesium-coated steel sheet is provided, including a substrate and a coating on the surface of the substrate. The parameters are shown in Table 3.

Table 3 Parameters of Al-Zn-Mg coated steel sheets of Comparative Examples 1-5

The preparation method of the above-mentioned aluminum-zinc-magnesium coated steel sheet is the same as the preparation method of Examples 1-7, and the parameters of the preparation method of each comparative example are shown in Table 4 respectively.

Table 4 Parameters of the preparation method of Comparative Examples 1-5

Experimental example 1

Corrosion evaluations were performed on the aluminum-zinc-magnesium-coated steel sheets provided in Examples 1-7 and Comparative Examples 1-5, respectively.

The operation method is as follows: put the galvanized steel sheet into the cyclic corrosion test box, conduct a cyclic corrosion test for one week, and then measure the mass loss of the coating before and after the test, and evaluate the corrosion resistance of the coating by the mass loss per unit area. The less mass loss, the better the corrosion resistance. The morphology of aluminum dendrites on the coating surface was analyzed by scanning electron microscope, and the size of aluminum dendrites was counted. Bend the coated steel sheet by 180 degrees, observe whether there are cracks on the bending surface, and observe whether the coating layer has poor adhesion such as peeling. The evaluation results are shown in the following table:

As can be seen from the above table, the coating quality of the aluminum-zinc-magnesium-coated steel sheets provided in Examples 1-7 of the present invention has significant advantages over Comparative Examples 1-5.

Finally, it should also be noted that the terms "comprising", "comprising" or any other variation thereof are intended to encompass a non-exclusive inclusion such that a process, method, article or device comprising a series of elements includes not only those elements, but also Also included are other elements not expressly listed or inherent to such a process, method, article or apparatus.

Although preferred embodiments of the present invention have been described, additional changes and modifications to these embodiments may occur to those skilled in the art once the basic inventive concepts are known. Therefore, the appended claims are intended to be construed to include the preferred embodiment and all changes and modifications that fall within the scope of the present invention.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. Thus, provided that these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims (10)

1. an aluminum-zinc-magnesium-coated steel sheet, characterized in that, comprising the coating on the substrate and the surface of the substrate, and the chemical composition of the coating comprises in mass percent; Al: 47-58%, Mg: 2-3%, Si: 1.5-2.5%, Ni: 0.05-0.80%, and the balance is Zn and inevitable impurities. 2 . The aluminum-zinc-magnesium coated steel sheet according to claim 1 , wherein an alloy layer is formed between the substrate and the coating layer, and the thickness of the alloy layer is 0.2-2 μm. 3 . 3 . The aluminum-zinc-magnesium-coated steel sheet according to claim 2 , wherein the mass percentage of Si in the alloy layer is greater than or equal to 10%. 4 . 4. The aluminum-zinc-magnesium-coated steel sheet according to any one of claims 1-3, wherein the surface layer of the substrate has oxides, and the volume percentage of the oxides is 0.1-5%; Wherein: the thickness of the surface layer is 1 μm. 5. a preparation method of the aluminum-zinc-magnesium-coated steel sheet as described in any one of claim 1-4, is characterized in that, comprises the steps: obtaining a slab of the substrate; subjecting the slab to heating, rough rolling, finishing rolling, coiling, first cooling, cold rolling and continuous annealing to obtain an annealed substrate; subjecting the annealed substrate to hot dip plating, second cooling and finishing to obtain the aluminum-zinc-magnesium-coated steel sheet; in: The chemical composition of the hot dip plating solution is the same as the chemical composition of the plating layer. 6 . The preparation method of the aluminum-zinc-magnesium coated steel sheet according to claim 5 , wherein the temperature of the coiling is 680-730° C. 7 . 7 . The method for preparing an aluminum-zinc-magnesium coated steel sheet according to claim 5 , wherein the first cooling rate is less than or equal to 1° C./s. 8 . 8 . The preparation method of the aluminum-zinc-magnesium coated steel sheet according to claim 5 , wherein the temperature of the continuous annealing is 750-850° C., and the dew point temperature of the continuous annealing is -10-10° C. 9 . 9 . The method for preparing an Al-Zn-Mg coated steel sheet according to claim 5 , wherein the temperature of the hot-dip plating solution is 530-580° C., and the hot-dip plating time is less than or equal to 60s. 10 . 10 . The preparation method of the aluminum-zinc-magnesium-coated steel sheet according to claim 5 , wherein the second cooling comprises cooling to 450° C. at a preset cooling rate, and the preset cooling rate is greater than or equal to 10° C./s. 11 .

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