Chromatic aberration-resistant high-corrosion-resistant hot-dip zinc-aluminum-magnesium coated steel plate and preparation method thereof

Abstract

The invention relates to an anti-chromatic-aberration high-corrosion-resistance hot-dip galvanized aluminum magnesium coated steel plate and a preparation method, and belongs to the technical field of coating and plating. The coated steel plate comprises a steel base body and a zinc-aluminum-magnesium coating attached to at least part of the surface of the steel base body. The chemical components of the zinc-aluminum-magnesium plating layer comprise Al, Mg, Bi, Sb and a matrix element Zn, the chemical components meet the following relations that [Sb + Bi] = (0.1-0.5) * [Mg], [Al-Mg] is larger than or equal to 12%, and [Mg] / [Al] is larger than or equal to 0.2, in the formulas, [Sb + Bi] represents the sum of the mass fractions of Sb and Bi, [Mg] represents the mass fraction of Mg, [Al-Mg] represents the difference of the mass fractions of Al and Mg, and [Mg] / [Al] represents the ratio of the mass fractions of Al and Mg; and the zinc-aluminum-magnesium plating layer contains an Mg-Bi compound and / or an Mg-Sb compound. The alloy components of the coating are improved, alloy elements Bi and Sb are introduced into the coating and are combined with a part of Mg to form Sb-Mg and Bi-Mg compounds, so that Mg compounds which are uniformly distributed are formed on the surface of the coating, and the color difference resistance of the zinc-aluminum-magnesium coating is remarkably improved.

Description

Technical Field

[0001] The present application relates to the field of coating technology, and particularly relates to a high-corrosion-resistant hot-dip galvanized aluminum-magnesium coating steel sheet with anti-color difference and a preparation method thereof. Background Art

[0002] Hot-dip galvanizing is to make the molten metal react with the iron matrix to produce an alloy layer, so that the matrix and the coating are combined. Hot-dip galvanized steel has the advantages of uniform coating, strong adhesion, long service life, simple manufacturing process, low product price, etc., and is widely used in the manufacture of automobile bodies, household appliances, etc. In order to improve the protection effect of the hot-dip galvanized coating on the cut position of the steel sheet and at the same time improve the planar corrosion resistance, an appropriate amount of Mg is added to the hot-dip coating to obtain a zinc-aluminum-magnesium coating, and the corrosion resistance can be further improved by more than 20%, and at the same time, the corrosion resistance of the processed cut position is available.

[0003] The zinc-aluminum-magnesium coating contains more magnesium elements. Magnesium is easy to react with oxidizing gases such as oxygen, water vapor, and carbon dioxide in the air to form a relatively thick magnesium-containing compound layer. This magnesium-containing compound layer is a mixture of magnesium oxides or / and hydroxides or / and basic carbonates. It is unstable in the initial stage of formation and presents a grayish-black color. However, this color change is often not uniform, so obvious color differences (hereinafter referred to as color differences) appear in different regions on the coating surface. This color difference affects the appearance quality of the product and cannot meet the user's requirements for the surface appearance of the product. Summary of the Invention

[0004] The present application provides a high-corrosion-resistant hot-dip galvanized aluminum-magnesium coating steel sheet with anti-color difference and a preparation method thereof to solve the following technical problem: how to improve the anti-color difference performance of the zinc-aluminum-magnesium coating.

[0005] In a first aspect, an embodiment of the present application provides a high-corrosion-resistant hot-dip galvanized aluminum-magnesium coating steel sheet with anti-color difference. The coating steel sheet includes a steel matrix and a zinc-aluminum-magnesium coating attached to at least part of the surface of the steel matrix;

[0006] The chemical composition of the zinc-aluminum-magnesium coating includes: Al, Mg, Bi, Sb, and the matrix element Zn, wherein the chemical composition satisfies the following relationship: [Sb + Bi] = (0.1 - 0.5) × [Mg], [Al - Mg] ≥ 12%, [Mg] / [Al] ≥ 0.2. In the formula, [Sb + Bi] represents the sum of the mass fractions of Sb and Bi, [Mg] represents the mass fraction of Mg, [Al - Mg] represents the difference between the mass fractions of Al and Mg, and [Mg] / [Al] represents the ratio of the mass fractions of Al and Mg;

[0007] The zinc-aluminum-magnesium coating contains Mg-Bi compounds and / or Mg-Sb compounds.

[0008] Optionally, the volume fraction of the Mg-Bi compound and / or the Mg-Sb compound is 0.01% to 1%.

[0009] Optionally, the volume fraction of the eutectic structure on the surface of the zinc-aluminum-magnesium coating is ≥50%.

[0010] Optionally, the area percentage of the binary eutectic structure in the zinc-aluminum-magnesium coating is ≤10%.

[0011] Optionally, the circumscribed circle diameter of the Mg-Bi compound and / or the Mg-Sb compound is ≤100 μm.

[0012] Optionally, by mass fraction, the chemical composition of the zinc-aluminum-magnesium coating includes: Al: 15% to 25%, Mg: 3% to 6%, [Bi + Sb]: 0.3% to 3%, and the matrix element Zn; wherein, [Bi + Sb] represents the sum of the mass fractions of Bi and Sb.

[0013] In a second aspect, an embodiment of the present application provides a method for preparing the anti-color-difference high-corrosion-resistant hot-dip galvanized aluminum-magnesium coating steel sheet described in the first aspect, and the method includes:

[0014] Performing hot-dip plating on the steel substrate to obtain a zinc-aluminum-magnesium coating steel sheet;

[0015] Cooling the zinc-aluminum-magnesium coating steel sheet.

[0016] Optionally, the plating solution temperature for the hot-dip plating is 450°C to 500°C.

[0017] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0018] An embodiment of the present application provides a high-corrosion-resistant hot-dip galvanized aluminum-magnesium coating steel sheet with anti-color difference. The coating steel sheet includes a steel substrate and a zinc-aluminum-magnesium coating attached to at least a part of the surface of the steel substrate. The chemical composition of the zinc-aluminum-magnesium coating includes: Al, Mg, Bi, Sb, and the matrix element Zn. Among them, the chemical composition satisfies the following relationships: [Sb + Bi] = (0.1 - 0.5) × [Mg], [Al - Mg] ≥ 12%, [Mg] / [Al] ≥ 0.2. In the formula, [Sb + Bi] represents the sum of the mass fractions of Sb and Bi, [Mg] represents the mass fraction of Mg, [Al - Mg] represents the difference between the mass fractions of Al and Mg, and [Mg] / [Al] represents the ratio of the mass fractions of Al and Mg. The zinc-aluminum-magnesium coating contains Mg-Bi compounds and / or Mg-Sb compounds. By improving the coating alloy composition, alloying elements Bi and Sb are introduced into the coating, combined with a part of Mg, to form Sb-Mg and Bi-Mg compounds, so that Mg compounds are evenly distributed on the coating surface, significantly improving the anti-color difference performance of the zinc-aluminum-magnesium coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings herein are incorporated into and constitute a part of this specification, showing embodiments consistent with the present application and, together with the specification, are used to explain the principles of the present application.

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 It is a schematic flow chart of a preparation method of a high-corrosion-resistant hot-dip galvanized aluminum-magnesium coating steel sheet with anti-color difference provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0023] Various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and individual values within that range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, which applies regardless of the range; in addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0024] In this text, terms including "comprising" etc. mean "including but not limited to". Relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "a plurality" means two or more; "at least one kind", "at least one of the following items (pieces)" or similar expressions refer to any combination of these items, including any combination of single item (piece) or plural items (pieces); for example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both mean: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. "Part number representation" such as weight part, mass part, etc. represents the proportional relationship between each component. In the proportional relationships involved in this text, the parameters that need to be described by proportion should be understood as the antecedents of the proportion formula in the order of description, and the proportional numbers should be understood as the consequents of the proportion formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportion formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0025] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in this text can be obtained through market purchase or can be prepared by existing methods.

[0026] In a first aspect, embodiments of the present application provide a high - corrosion - resistant hot - dip galvanized aluminum - magnesium coating steel sheet with anti - color difference, and the coating steel sheet includes a steel substrate and a zinc - aluminum - magnesium coating attached to at least a part of the surface of the steel substrate;

[0027] The chemical composition of the zinc-aluminum-magnesium coating includes: Al, Mg, Bi, Sb, and the matrix element Zn. Among them, the chemical composition satisfies the following relationships: [Sb + Bi] = (0.1 - 0.5) × [Mg], [Al - Mg] ≥ 12%, [Mg] / [Al] ≥ 0.2. In the formula, [Sb + Bi] represents the sum of the mass fractions of Sb and Bi, [Mg] represents the mass fraction of Mg, [Al - Mg] represents the difference between the mass fractions of Al and Mg, and [Mg] / [Al] represents the ratio of the mass fractions of Al and Mg;

[0028] The zinc-aluminum-magnesium coating contains Mg-Bi compounds and / or Mg-Sb compounds.

[0029] The anti-chromatic aberration high-corrosion-resistant hot-dip galvanized aluminum-magnesium coating steel sheet provided by the embodiment of the present application includes a steel substrate and a zinc-aluminum-magnesium coating attached to at least a part of the surface of the steel substrate. There is no special limitation on the steel substrate, and ordinary steel sheets such as hot-rolled steel sheets and cold-rolled steel sheets can be used. There is also no special limitation on the steel grade, and for example, aluminum-killed steel, extra-low-carbon steel, and high-strength steel can be used.

[0030] The purpose of adding Bi and Sb in the embodiment of the present application is to consume Mg in the coating to form Sb-Mg and Bi-Mg compounds. Therefore, the addition amount is related to the mass fraction of Mg in the coating. If too little is added, insufficient Sb-Mg and Bi-Mg compounds cannot be formed; however, if too much is added, a large amount of large-sized Mg-Sb and Mg-Bi compounds will be formed. Experiments have found that it is most beneficial that the total mass fraction of Sb and Bi is 10% to 50% of the mass fraction of Mg. Therefore, in the embodiment of the present application, the chemical composition of the zinc-aluminum-magnesium coating satisfies: [Sb + Bi] = (0.1 - 0.5) × [Mg]. In the formula, [Sb + Bi] represents the sum of the mass fractions of Sb and Bi, and [Mg] represents the mass fraction of Mg.

[0031] The eutectic structure is divided into a ternary eutectic structure and a binary eutectic structure. Mg in the zinc-aluminum-magnesium coating is concentrated in the eutectic structure. The ternary eutectic structure includes an aluminum-rich phase, a zinc-rich phase, and a magnesium-zinc compound, such as Mg2Zn 11, MgZn2, etc. In the binary eutectic structure, there are usually only magnesium-zinc compounds and zinc-rich or aluminum-rich phases. To form a uniformly dispersed eutectic structure, the mass fraction of Mg relative to Al in the coating cannot be too high, otherwise large chunks of the binary eutectic structure are likely to appear. Therefore, it is required that the mass fraction of Al in the coating is 12% or more higher than the mass fraction of Mg, so that the area percentage of the binary eutectic structure does not exceed 10%. Therefore, in the embodiments of the present application, the chemical composition of the zinc-aluminum-magnesium coating satisfies: [Al - Mg] ≥ 12%, where [Al - Mg] represents the difference in the mass fractions of Al and Mg. Exemplarily, the difference in the mass fractions of Al and Mg can be 12%, 14%, 16%, 18%, 20%, etc.

[0032] The mass fraction of Mg in the coating cannot be too low, especially relative to Al. If the mass fraction of Mg is too low relative to the mass fraction of Al, a double-layer hydroxide protective film of Mg and Al cannot be formed during the corrosion process of the coating, and the corrosion resistance of the coating decreases. Therefore, in the embodiments of the present application, the chemical composition of the zinc-aluminum-magnesium coating satisfies: [Mg] / [Al] ≥ 0.2, where [Mg] / [Al] represents the ratio of the mass fractions of Al and Mg. Exemplarily, the ratio of the mass fractions of Al and Mg can be 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, etc.

[0033] Zn is the matrix element, and the specific content / content range of Zn can be obtained through the upper and lower limit formulas of the components, that is:

[0034] The sum of the percentage contents of each component in a composition should be equal to 100%. The content ranges of several components should meet the following conditions: the upper limit value of a certain component + the lower limit values of other components ≤ 100; the lower limit value of a certain component + the upper limit values of other components ≥ 100.

[0035] In some embodiments, the volume fraction of the Mg-Bi compound and / or the Mg-Sb compound is 0.01% - 1%.

[0036] Exemplarily, the volume fraction of the Mg-Bi compound and / or the Mg-Sb compound can be 0.01%, 0.05%, 0.1%, 0.5%, 1%, etc.

[0037] In some embodiments, the volume fraction of the surface eutectic structure of the zinc-aluminum-magnesium coating can be ≥ 50%.

[0038] In the atmosphere, especially in a relatively humid atmosphere, a thin liquid film adheres to the surface of the zinc-aluminum-magnesium coating. The oxygen enriched in the thin liquid film preferentially undergoes an electrochemical reaction with magnesium in the coating, rapidly forming magnesium compounds. These magnesium compounds exhibit a gray appearance. If the magnesium compounds formed on the coating surface are macroscopically non-uniform, it will result in different colors at different positions on the surface, thereby causing surface color difference. Magnesium in the coating often exists in the eutectic structure in the form of compounds. If the eutectic structure of the coating occupies a relatively large area ratio, the distribution of the eutectic structure is likely to be uniform in space. The uniformly distributed eutectic structure can make the surface compounds of magnesium more uniform, reducing the occurrence of color difference. Therefore, in the embodiments of this application, it is required that the volume fraction of the surface eutectic structure of the coating is not less than 50%. Exemplarily, the volume fractions of the surface eutectic structure of the zinc-aluminum-magnesium coating are 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc.

[0039] In some embodiments, the area percentage of the binary eutectic structure in the zinc-aluminum-magnesium coating ≤ 10%.

[0040] If the area ratio of the binary eutectic structure is higher than 10%, the reaction rate difference between the binary eutectic structure and the ternary eutectic structure is relatively large, resulting in local color difference problems. At the same time, when the content of the binary eutectic structure is higher than 10%, it also causes the coating to be too brittle. Exemplarily, the area percentages of the binary eutectic structure in the zinc-aluminum-magnesium coating can be 2%, 4%, 6%, 8%, 10%, etc.

[0041] In some embodiments, the circumscribed circle diameter of the Mg-Bi compound and / or Mg-Sb compound ≤ 100 μm.

[0042] If large-sized Mg-Sb and Mg-Bi compounds are formed, it will cause an increase in the brittleness of the coating. Therefore, it is required that the circumscribed circle diameter of the formed Mg-Sb and Mg-Bi compounds does not exceed 100 μm. Exemplarily, the circumscribed circle diameters of the Mg-Bi compound and / or Mg-Sb compound can be 20 μm, 40 μm, 60 μm, 80 μm, 100 μm, etc.

[0043] In some embodiments, by mass fraction, the chemical composition of the zinc-aluminum-magnesium coating includes: Al: 15% - 25%, Mg: 3% - 6%, [Bi + Sb]: 0.3% - 3%, and the matrix element Zn; where [Bi + Sb] represents the sum of the mass fractions of Bi and Sb.

[0044] The zinc-aluminum-magnesium coating is formed on the surface of the steel substrate. The chemical composition of this coating includes: Al: 15% - 25%, Mg: 3% - 6%, Bi + Sb: 0.3% - 3%, and the matrix element Zn; among them, Bi + Sb represents the sum of the mass fractions of Bi and Sb. The zinc-aluminum-magnesium coating is usually manufactured by the hot-dip plating process, and the liquid zinc-aluminum-magnesium alloy solidifies on the surface of the steel plate to form the coating.

[0045] Adding more element Al to the zinc-aluminum-magnesium coating, some Al can precipitate first to form α-Al dendritic crystals during the solidification of the coating. This kind of α-Al dendritic crystal has high corrosion resistance. In addition, according to the Al-Zn phase diagram, the remaining Al will precipitate into β-Al(Zn) phase and η-Zn(Al) phase during the further solidification and cooling of the coating. The appearance of this η-Zn(Al) phase will lead to a decrease in the corrosion resistance of the coating. Therefore, efforts should be made to reduce the appearance of the η-Zn(Al) phase and increase the α-Al phase. Therefore, the mass fraction of Al in the coating cannot be too low. In the embodiments of this application, it is required that the mass fraction of Al is not less than 15%. However, after the mass fraction of Al in the coating exceeds 25%, obvious solid-phase segregation reactions occur during the solidification of the coating. Since the segregation reaction requires long-distance diffusion in the solid state, the phase change kinetics is too difficult and usually difficult to complete. This leads to a large amount of non-steady β-Al(Zn) phase in the coating, and the corrosion resistance decreases significantly. Therefore, the mass fraction of Al in the coating cannot be too high. Experiments show that the mass fraction of Al cannot exceed 25%. Exemplarily, the mass fraction of Al in the zinc-aluminum-magnesium coating can be 15%, 17%, 19%, 21%, 23%, 25%, etc.

[0046] Element Mg in the coating can significantly improve the atmospheric 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, react with the dissolved carbon dioxide in the water film, and precipitate a dense protective film. This protective film can stably exist in neutral and weakly alkaline environments, and at the same time can also promote the electrolyte solution on the surface of the coating to become a weakly alkaline solution, thereby improving the corrosion resistance of the coating. If the mass fraction of Mg in the coating is lower than 3%, the corrosion resistance of the coating will decrease significantly. However, if the mass fraction of Mg in the coating is higher than 6%, there will be more Mg-rich HCP phases. This kind of phase is a brittle phase and is prone to cause cracking and peeling of the coating during the processing of the zinc-aluminum-magnesium coating. Exemplarily, the mass fraction of Mg in the zinc-aluminum-magnesium coating can be 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, etc.

[0047] Mg in zinc-aluminum-magnesium coatings mainly exists in the form of Mg-Zn compounds. Mg-Zn compounds have very low electrochemical potentials and react quickly in the air to form surface oxides, hydroxides, carbonates and other compounds of Mg. The reaction rate is too fast, resulting in macroscopic unevenness. If other relatively inert alloying elements such as Bi and Sb are introduced into the coating, combined with a portion of Mg, the reaction rate can be slowed down. As a result, more uniformly distributed Mg compounds, including oxides, hydroxides or carbonates, are formed on the surface. Therefore, a small amount of elements Bi and Sb are added to the coating. Bi+Sb is not less than 0.3%, so that the volume fraction range of Bi-Mg and Sb-Mg compounds is not less than 0.01%. If the volume fraction of Bi-Mg and Sb-Mg compounds is less than 0.01%, no beneficial effect can be achieved. However, if Bi and Sb are added in excess of 3%, a large amount of bulky Mg-Sb and Mg-Bi compounds will be formed in the coating. This compound is too brittle, which makes it easy to cause cracking and peeling of the zinc-aluminum-magnesium coating during processing. Therefore, the embodiment of the present application requires that the mass fraction of Bi+Sb does not exceed 3%, so that the volume fraction of the compound does not exceed 1%. For example, the sum of the mass fractions of Bi and Sb in the zinc-aluminum-magnesium coating can be 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0048] Figure 1 A schematic flow chart of a method for preparing a color-difference-resistant, highly corrosion-resistant hot-dip galvanized aluminum-magnesium coated steel plate provided in an embodiment of the present application.

[0049] See also Figure 1 In a second aspect, an embodiment of the present application provides a method for preparing a color-difference-resistant, highly corrosion-resistant hot-dip galvanized aluminum-magnesium coated steel sheet as described in the first aspect, the method comprising:

[0050] S1, hot-dip plating the steel substrate to obtain a zinc-aluminum-magnesium coated steel plate;

[0051] S2, cooling the zinc-aluminum-magnesium coated steel plate.

[0052] In some embodiments, the bath temperature of the hot-dip plating is 450°C to 500°C.

[0053] In the manufacturing process of zinc-aluminum-magnesium coated steel sheets, the hot-dip plating process plays an important role in the coating structure. During the hot-dip plating process, if the temperature of the plating solution is too low, a large number of large binary eutectic structures are likely to appear in the coating. However, if the plating solution temperature is too high, coarse and massive Mg-Bi and Mg-Sb phases will be formed in the coating. In this way, the effects of the Mg-Bi and Mg-Sb phases are weakened, and at the same time, the brittleness of the coating is caused. Therefore, the temperature of the plating solution should not exceed 500 °C. Exemplarily, the plating solution temperature for hot-dip plating can be 450 °C - 500 °C, etc.

[0054] The product prepared by the preparation method of the anti-color difference and highly corrosion-resistant hot-dip galvanized aluminum-magnesium coated steel sheet is the above-mentioned anti-color difference and highly corrosion-resistant hot-dip galvanized aluminum-magnesium coated steel sheet. Since the preparation method of the anti-color difference and highly corrosion-resistant hot-dip galvanized aluminum-magnesium coated steel sheet adopts some or all of the technical solutions of the embodiments of the anti-color difference and highly corrosion-resistant hot-dip galvanized aluminum-magnesium coated steel sheet, it at least has all the beneficial effects brought by the technical solutions of the anti-color difference and highly corrosion-resistant hot-dip galvanized aluminum-magnesium coated steel sheet, which will not be elaborated one by one here.

[0055] The following will further elaborate on the present application in combination with specific embodiments. The experimental methods without specific conditions indicated in the following embodiments are usually determined according to national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out according to general international standards, conventional conditions or the conditions recommended by the manufacturer.

[0056] Steel sheets with a thickness of 1.0 mm and a width of 1500 mm are used as the substrate, and the coating weight is 100 grams per square meter on both sides. The characteristics of Examples 1-13 and Comparative Examples 1-5 of the present application are shown in Table 1.

[0057] Table 1

[0058]

[0059]

[0060] The preparation process conditions of Examples 1-13 and Comparative Examples 1-5 of the present application are shown in Table 2.

[0061] An anti-color difference performance evaluation experiment was conducted on the zinc-aluminum-magnesium coated steel sheets prepared in the above Examples 1-13 and Comparative Examples 1-5: The zinc-aluminum-magnesium coated steel sheets were surface-treated to remove the oxide film layer on the surface, and the surface brightness L0 of the zinc-aluminum-magnesium coated steel sheets after removing the oxide film layer was measured. Then, test samples of the zinc-aluminum-magnesium coated steel sheets were obtained. The test samples of the zinc-aluminum-magnesium coated steel sheets were made into laminations and then stored in a damp and hot environment for a period of time. Then, they were taken out, and the surface brightness L1 of the test samples of the zinc-aluminum-magnesium coated steel sheets was measured. Calculate ΔL = L0 - L1, and evaluate the blackening tendency of the zinc-aluminum-magnesium coating according to the magnitude of ΔL. The specific experimental method refers to the invention patent ZL202110169281.3. If ΔL is not greater than 8, the anti-color difference performance is excellent If ΔL exceeds 8, the anti-color difference performance is poor (×).

[0062] The coating brittleness of the zinc-aluminum-magnesium coated steel sheets prepared in the above Examples 1-13 and Comparative Examples 1-5 was evaluated: By the bending method, the sample piece was bent 180°, and then the cracking and peeling of the coating at the bending position were observed. If coating cracking or peeling occurred at the bending position, the coating brittleness was poor (×), otherwise the coating brittleness was excellent

[0063] A neutral salt spray test was conducted on the zinc-aluminum-magnesium coated steel sheets prepared in the above Examples 1-13 and Comparative Examples 1-5. The average thickness of the coating before corrosion and the average thickness of the coating after corrosion of the zinc-aluminum-magnesium coated steel sheets were measured, the difference between the two was calculated, and then divided by the corrosion time to obtain the average corrosion rate of the coating

[0064] Average corrosion rate = (average thickness of the coating before corrosion - average thickness of the coating after corrosion) / corrosion time (μm / h).

[0065] If the average corrosion rate of the coating does not exceed 0.015 μm / h, the corrosion resistance of the coating is excellent If the average corrosion rate of the coating exceeds 0.015 μm / h, the corrosion resistance of the coating is poor (×).

[0066] The experimental evaluation results are shown in Table 2

[0067] Table 2

[0068]

[0069]

[0070] As can be seen from Table 2, the zinc-aluminum-magnesium coated steel sheets provided in the examples of the present application have excellent color difference performance and excellent corrosion resistance on the surface

[0071] One or more technical solutions in the embodiments of the present invention at least further have the following technical effects or advantages:

[0072] The hot-dip galvanized aluminum-magnesium plated steel sheet with anti-color difference and high corrosion resistance provided by the embodiment of the present invention has good anti-color difference properties in the atmospheric exposure environment and extremely high corrosion resistance at the same time.

[0073] The preparation method of the hot-dip galvanized aluminum-magnesium plated steel sheet with anti-color difference and high corrosion resistance provided by the embodiment of the present invention has the effects of being simple and easy to operate, having low production costs, and being easy to promote and use.

[0074] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but will conform to the widest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A highly corrosion-resistant hot-dip zinc-aluminum-magnesium coated steel sheet with anti-color difference, the coated steel sheet comprising a steel substrate and a zinc-aluminum-magnesium coating attached to at least a portion of the surface of the steel substrate; The chemical composition of the zinc-aluminum-magnesium coating includes: Al, Mg, Bi, Sb and matrix element Zn, wherein the chemical composition satisfies the following relationship: [Sb+Bi]=(0.1-0.5)×[Mg], [Al-Mg]≥12%, [Mg] / [Al]≥0.2, wherein [Sb+Bi] represents the sum of the mass fractions of Sb and Bi, [Mg] represents the mass fraction of Mg, [Al-Mg] represents the difference between the mass fractions of Al and Mg, and [Mg] / [Al] represents the ratio of the mass fractions of Al and Mg; The zinc-aluminum-magnesium coating contains Mg-Bi compound and / or Mg-Sb compound.

2. The coated steel sheet according to claim 1, characterized in that: The volume fraction of the Mg-Bi compound and / or the Mg-Sb compound is 0.01% to 1%.

3. The coated steel sheet according to claim 1, characterized in that: The volume fraction of the surface eutectic structure of the zinc-aluminum-magnesium coating is ≥50%.

4. The coated steel sheet according to claim 1, characterized in that: The area percentage of the binary eutectic structure in the zinc-aluminum-magnesium coating is ≤10%.

5. The coated steel sheet according to claim 1, characterized in that: The circumscribed circle diameter of the Mg-Bi compound and / or the Mg-Sb compound is ≤100 μm.

6. The coated steel sheet according to claim 1, characterized in that: In terms of mass fraction, the chemical composition of the zinc-aluminum-magnesium coating includes: Al: 15% to 25%, Mg: 3% to 6%, [Bi+Sb]: 0.3% to 3%, and matrix element Zn; wherein [Bi+Sb] represents the sum of the mass fractions of Bi and Sb.

7. A method for preparing the anti-color-difference and highly corrosion-resistant hot-dip galvanized aluminum-magnesium coated steel sheet according to any one of claims 1 to 6, the method comprising: Hot-dip coating the steel substrate to obtain a zinc-aluminum-magnesium coated steel plate; The zinc-aluminum-magnesium coated steel sheet is cooled.

8. The method according to claim 7, characterized in that The bath temperature of the hot-dip plating is 450°C to 500°C.

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