A zinc-aluminum-magnesium coated steel sheet and its preparation method

Abstract

This application relates to a zinc-aluminum-magnesium coated steel sheet and its preparation method, belonging to the field of zinc-aluminum-magnesium coated steel sheets. The technical problem solved by this application is that the surface of zinc-aluminum-magnesium coated steel sheets is prone to blackening and it is difficult to maintain the metallic luster in the prior art. The technical solution adopted in this application is to immerse the zinc-aluminum-magnesium coated steel sheet in an aqueous solution containing benzotriazole for a certain period of time, thereby forming a benzotriazole-based complex layer on the surface of the zinc-aluminum-magnesium coated steel sheet. This complex reacts chemically with the coating surface, thereby protecting the steel sheet surface and reducing the corrosion rate of the cathode and anolyte in the presence of water. The method provided by this application can improve the surface blackening resistance of zinc-aluminum-magnesium coated steel sheets and effectively maintain the metallic luster of zinc-aluminum-magnesium coated steel sheets.

Description

Technical Field

[0001] This application relates to the field of zinc-aluminum-magnesium coated steel sheets, and more particularly to a zinc-aluminum-magnesium coated steel sheet and its preparation method. Background Technology

[0002] Hot-dip galvanized aluminum-magnesium coated steel sheets possess a delicate metallic luster and excellent corrosion resistance, primarily used in the production of building decoration materials, electrical appliance housings, and agricultural and livestock machinery parts. In recent years, various types of hot-dip galvanized aluminum-magnesium coated steel sheets have emerged. Among them, high-aluminum zinc-aluminum-magnesium products, with an aluminum content exceeding 50% and the addition of a certain amount of magnesium, exhibit superior surface and cut-edge corrosion resistance compared to ordinary coated products, demonstrating significant social benefits and widespread application value.

[0003] However, zinc-aluminum-magnesium coated steel sheets are prone to blackening, which damages the metallic luster and affects the product's appearance, thus greatly limiting the promotion and use of zinc-aluminum-magnesium coated steel sheets. Summary of the Invention

[0004] This application provides a zinc-aluminum-magnesium coated steel sheet and its preparation method to solve the technical problem of blackening and difficulty in maintaining metallic luster on the surface of zinc-aluminum-magnesium coated steel sheets in the prior art.

[0005] In a first aspect, this application provides a method for preparing zinc-aluminum-magnesium coated steel sheet, the method comprising:

[0006] A steel substrate is placed in a plating solution containing a set chemical composition to obtain a zinc-aluminum-magnesium coated steel sheet.

[0007] Cool the zinc-aluminum-magnesium coated steel sheet to a first set temperature;

[0008] The soaking solution containing benzotriazole is heated to the second set temperature;

[0009] The cooled zinc-aluminum-magnesium coated steel sheet is placed in the heated immersion solution and immersed for a set duration.

[0010] The zinc-aluminum-magnesium coated steel sheet after immersion is subjected to chromium-free passivation treatment.

[0011] Optionally, the mass concentration of the benzotriazole is 0.5 g / L to 1 g / L.

[0012] Optionally, the soaking solution further includes at least one of the following: sodium benzoate, sodium dodecylbenzenesulfonate, and

[0013] Methylbenzotriazole.

[0014] Optionally, the mass concentration of the methylbenzotriazole is 0.05 g / L to 0.2 g / L; and / or

[0015] The mass concentration of the sodium benzoate is 1 g / L-5 g / L; and / or

[0016] The mass concentration of the sodium dodecylbenzenesulfonate is between 0.3 g / L and 1 g / L.

[0017] Optionally, the first set temperature is set to 120℃-180℃.

[0018] Optionally, the second set temperature is 35℃-60℃.

[0019] Optionally, the set duration is 1 min to 10 min.

[0020] Optionally, the chemical composition of the plating solution includes:

[0021] Mg: 0.7 wt% - 1.1 wt%, Al: 55 wt% - 56 wt%, Si: 1.5 wt% - 1.6 wt%, Zn.

[0022] In a second aspect, this application provides a zinc-aluminum-magnesium coated steel sheet, which is prepared by any one of the methods in the first aspect. The steel sheet includes a steel substrate, a zinc-aluminum-magnesium coating covering the surface of the steel substrate, a benzotriazole-based complex layer covering the surface of the zinc-aluminum-magnesium coating, and a chromium-free passivation layer covering the surface of the benzotriazole-based complex layer.

[0023] Optionally, the chemical composition of the zinc-aluminum-magnesium coating includes: Mg: 0.7 wt%-1.1 wt%, Al: 55 wt%-56 wt%, Si: 1.5 wt%-1.6 wt%, Zn.

[0024] The technical solutions provided in this application have the following advantages compared with the prior art:

[0025] The method provided in this application involves immersing a zinc-aluminum-magnesium coated steel sheet in an aqueous solution containing benzotriazole for a certain period of time, thereby forming a benzotriazole-based complex layer on the surface of the zinc-aluminum-magnesium coated steel sheet. This complex interacts with the coating surface through chemical adsorption, thus protecting the steel sheet surface and reducing the corrosion rates of the cathode and anolyte in the presence of water. This improves the blackening resistance of the zinc-aluminum-magnesium coated surface and effectively solves the technical problem of blackening and difficulty in maintaining metallic luster on the surface of zinc-aluminum-magnesium coated steel sheets in the prior art. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A schematic flowchart illustrating the preparation method of the zinc-aluminum-magnesium coated steel sheet provided in the embodiments of this application;

[0029] Figure 2 This is a schematic diagram of the zinc-aluminum-magnesium coated steel sheet provided in the embodiments of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0032] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical 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 single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0033] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the orientation shown in the accompanying drawings. Furthermore, in the description of this application, the terms "comprising" and "including" mean "including but not limited to".

[0034] In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any actual relationship or order between these entities or operations. In this document, "and / or" describes the association between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0035] The technical solution provided in this application is to solve the above-mentioned technical problems, and the overall approach is as follows:

[0036] In a first aspect, this application provides a method for preparing zinc-aluminum-magnesium coated steel sheet, the method comprising:

[0037] A steel substrate is placed in a plating solution containing a set chemical composition to obtain a zinc-aluminum-magnesium coated steel sheet.

[0038] Cool the zinc-aluminum-magnesium coated steel sheet to a first set temperature;

[0039] The soaking solution containing benzotriazole is heated to the second set temperature;

[0040] The cooled zinc-aluminum-magnesium coated steel sheet is placed in the heated immersion solution and immersed for a set duration.

[0041] The zinc-aluminum-magnesium coated steel sheet after immersion is subjected to chromium-free passivation treatment.

[0042] In this embodiment, the immersion solution contains benzotriazole. Benzotriazole can form benzotriazole-based complexes with zinc and aluminum in the zinc-aluminum-magnesium coating, resulting in chemical adsorption on the coating surface. This reduces the corrosion rate of the cathode and anolyte, thereby improving the blackening phenomenon of the zinc-aluminum-magnesium coating surface in the presence of water. Moreover, the benzotriazole-based complex layer is colorless and transparent, and does not affect the metallic luster of the zinc-aluminum-magnesium coated steel sheet.

[0043] In this embodiment, chromium-free passivation is used. Chromium-free passivation does not contain hexavalent or trivalent chromium, which has carcinogenic effects. It is environmentally friendly, has good corrosion resistance, and does not damage the benzotriazole-based complex layer, thereby improving the surface blackening resistance of the zinc-aluminum-magnesium coating while maintaining the metallic luster.

[0044] In some embodiments, the mass concentration of benzotriazole is 0.5 g / L to 1 g / L.

[0045] In this embodiment, if the concentration of benzotriazole is too low, it will not be sufficient to form a benzotriazole-based complex. If the concentration of benzotriazole is too high, a complex with high solubility may be generated, which will dissolve the original insoluble complex layer, thereby reducing the inhibitory effect on blackening.

[0046] In some embodiments, the soaking solution further includes at least one of the following: sodium benzoate, sodium dodecylbenzenesulfonate, and

[0047] Methylbenzotriazole.

[0048] In this embodiment, the soaking solution contains sodium benzoate, which can have an effective synergistic effect with benzotriazole, promoting the adsorption of benzotriazole-based complexes formed by benzotriazole and metal ions onto the metal surface, thereby improving the blackening phenomenon of zinc-aluminum-magnesium coatings in the presence of water.

[0049] In this embodiment, the soaking solution contains sodium dodecylbenzenesulfonate. Sodium dodecylbenzenesulfonate, as an anionic surfactant, can improve the uniformity of the benzotriazole-based complex layer and improve the blackening phenomenon of the zinc-aluminum-magnesium coating surface in the presence of water.

[0050] In this embodiment, the immersion solution contains methylbenzotriazole. Methylbenzotriazole and benzotriazole are homologues. The combination of the two can better form benzotriazole-based complexes with zinc and aluminum, and promote the chemical adsorption of the complexes to the coating surface, reduce the corrosion rate of the cathode and anode, and improve the blackening phenomenon of the zinc-aluminum-magnesium coating surface in the presence of water.

[0051] In some embodiments, the mass concentration of the methylbenzotriazole is 0.05 g / L to 0.2 g / L; and / or

[0052] The mass concentration of the sodium benzoate is 1 g / L-5 g / L; and / or

[0053] The mass concentration of the sodium dodecylbenzenesulfonate is between 0.3 g / L and 1 g / L.

[0054] In this embodiment, if the sodium benzoate concentration is too low, sodium benzoate and benzotriazole cannot produce an effective synergistic effect; if the sodium benzoate concentration is too high, a complex with high solubility may be formed, causing the original poorly soluble benzotriazole-based complex layer to dissolve, thus reducing the inhibitory effect on blackening.

[0055] In this embodiment, if the sodium dodecylbenzenesulfonate concentration is too low, it is insufficient to improve the uniformity of the complex layer; if the sodium dodecylbenzenesulfonate concentration is too high, it will coat the surface of the complex layer, resulting in a poorer film-forming effect.

[0056] In this embodiment, if the concentration of methylbenzotriazole is too low, the complex will not be able to reduce the corrosion rate; if the concentration of methylbenzotriazole is too high, the adsorption of the complex to the coating surface may be reduced, thus reducing the inhibition of blackening.

[0057] In some embodiments, the first set temperature is 120℃-180℃.

[0058] In this embodiment, the temperature of the zinc-aluminum-magnesium coated steel sheet needs to be between 120°C and 180°C before immersion in the immersion solution containing benzotriazole. Too low a temperature affects the surface activity of the steel sheet, making it difficult for benzotriazole-based complexes to form; too high a temperature makes the benzotriazole-based complex layer loose, reducing its protective effect on the steel sheet.

[0059] In some embodiments, the second set temperature is 35℃-60℃.

[0060] In this embodiment, if the aqueous solution temperature is too low, it is not easy to obtain a complete benzotriazole-based complex layer; if the aqueous solution temperature is too high, the benzotriazole-based complex layer will easily become loose.

[0061] In some embodiments, the set duration is 1 min to 10 min.

[0062] In this embodiment, if the soaking time is too short, it is not easy to obtain a complete benzotriazole-based complex layer; if the soaking time is too long, it will affect the production efficiency.

[0063] In some embodiments, the chemical composition of the plating solution includes:

[0064] Mg: 0.7 wt% - 1.1 wt%, Al: 55 wt% - 56 wt%, Si: 1.5 wt% - 1.6 wt%, Zn.

[0065] In this embodiment, the mass fraction of Mg is 0.7 wt%-1.1 wt%. Within this mass fraction range, Mg ensures the formation of the Mg2Si phase with Si, the formation of the MgZn2 phase with Zn, and the formation of a ternary eutectic phase with Zn and Al. This ensures that the zinc-aluminum-magnesium coated steel sheet has excellent planar corrosion resistance and cut-edge corrosion resistance. When the mass fraction value is greater than or less than the endpoint of this range, the adverse effects are as follows: if the value is too large, the formed Mg2Si phase will be large, affecting the coating's forming performance; the MgZn2 phase formed by Mg and Zn will be abundant on the surface, affecting the coating's resistance to blackening. If the value is too small, the Mg2Si phase, MgZn2 phase, and the ternary eutectic phase formed by Mg with Zn and Al will be insufficient, affecting the coating's corrosion resistance.

[0066] In this embodiment, the mass fraction of Al is 55%-56% by weight. Within this mass fraction range, Al can ensure the formation of a ternary eutectic phase with Mg and Zn, thereby ensuring that the zinc-aluminum-magnesium coated steel sheet has excellent planar corrosion resistance and cut corrosion resistance. When the mass fraction value is greater than or less than the endpoint of this range, the adverse effects are: if the value is too large, the proportion of Al phase is too high, which will affect the uniformity and corrosion resistance of the coating; if the value is too small, the ternary eutectic phase cannot be formed, which will affect the corrosion resistance of the coating.

[0067] In this embodiment, the mass fraction of Si is 1.5%-1.6% by weight. Within this mass fraction range, Si can ensure the formation of the Mg2Si phase with Mg, while also ensuring that the thickness of the alloy layer between the coating and the substrate is within a reasonable range. When the mass fraction value is greater than or less than the endpoint of this range, the adverse effects are: if the value is too large, the formed Mg2Si will be coarse, which will affect the forming performance of the coating; if the value is too small, the alloy layer will be too thick, which will affect the forming performance of the coating.

[0068] Secondly, embodiments of this application also provide a zinc-aluminum-magnesium coated steel sheet, said steel sheet being prepared by any one of the methods described in the first aspect, such as... Figure 2 As shown, the steel plate includes a steel substrate, a zinc-aluminum-magnesium coating covering the surface of the steel substrate, a benzotriazole-based complex layer covering the surface of the zinc-aluminum-magnesium coating, and a chromium-free passivation layer covering the surface of the benzotriazole-based complex layer.

[0069] In some embodiments, the chemical composition of the zinc-aluminum-magnesium coating includes: Mg: 0.7 wt%-1.1 wt%, Al: 55 wt%-56 wt%, Si: 1.5 wt%-1.6 wt%, Zn.

[0070] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0071] Relevant experimental and effect data:

[0072] The preparation methods of the zinc-aluminum-magnesium coated steel sheets used in Examples 1-6 are as follows: Figure 1 As shown, the specific steps are as follows:

[0073] S1. Immerse the steel substrate in liquid metal for hot-dip galvanizing to obtain zinc-aluminum-magnesium coated steel sheet;

[0074] S2. Cool the aluminum-magnesium coated steel sheet;

[0075] S3. The cooled zinc-aluminum-magnesium coated steel sheet is immersed in an aqueous solution containing benzotriazole to obtain a zinc-aluminum-magnesium coated steel sheet with a benzotriazole-based complex layer on its surface.

[0076] S4. The zinc-aluminum-magnesium coated steel sheet with a benzotriazole-based complex layer on its surface is dried;

[0077] S5. The dried zinc-aluminum-magnesium coated steel sheet with a benzotriazole-based complex layer on its surface is subjected to chromium-free passivation treatment to obtain a zinc-aluminum-magnesium coated steel sheet with metallic luster and no surface blackening.

[0078] The method for preparing the zinc-aluminum-magnesium coated steel sheet used in Comparative Example 1 is as follows:

[0079] The steel substrate is subjected to hot-dip galvanizing, cooling, and chromium-free passivation treatment to obtain zinc-aluminum-magnesium coated steel sheet.

[0080] S1. Immerse the steel substrate in liquid metal for hot-dip galvanizing to obtain zinc-aluminum-magnesium coated steel sheet;

[0081] S2. Cool the aluminum-magnesium coated steel sheet;

[0082] S3. The cooled zinc-aluminum-magnesium coated steel sheet is subjected to chromium-free passivation treatment to obtain zinc-aluminum-magnesium coated steel sheet.

[0083] The preparation method steps of the zinc-aluminum-magnesium coated steel sheet used in Comparative Example 2 are as follows:

[0084] S1. Immerse the steel substrate in liquid metal for hot-dip galvanizing to obtain zinc-aluminum-magnesium coated steel sheet;

[0085] S2. Cool the aluminum-magnesium coated steel sheet;

[0086] S3. The cooled zinc-aluminum-magnesium coated steel sheet is immersed in an aqueous solution containing chloride and sulfate ions and then subjected to chromium-free passivation treatment to obtain the zinc-aluminum-magnesium coated steel sheet.

[0087] The specific chemical compositions and parameters of Examples 1-6 and Comparative Examples 1-2 are as follows:

[0088] 1. The chemical composition (mass percentage) of the molten metal liquid used for hot-dip plating in Examples 1-6 and Comparative Examples 1-2 is shown in Table 1, with the remainder being Zn and unavoidable impurity elements:

[0089] Table 1

[0090] Example 1 1.1 55 1.6 Example 2 1.0 56 1.5 Example 3 0.9 55 1.6 Example 4 1.0 56 1.5 Example 5 0.8 55 1.6 Example 6 0.7 55 1.6 Comparative Example 1 1.2 55 1.6 Comparative Example 2 1.2 55 1.6

[0091] 2. The composition of the benzotriazole-containing soaking solution involved in the preparation methods of Examples 1-6 is shown in Table 2, with the remainder being deionized water:

[0092] Table 2

[0093]

[0094] 3. The soaking process in an aqueous solution containing benzotriazole involved in the preparation methods of Examples 1-6 is shown in Table 3:

[0095] Table 3

[0096]

[0097]

[0098] Related experiments:

[0099] The steel plates obtained in Examples 1-6 and Comparative Examples 1-2 were sampled respectively. The surface brightness L value of the steel plates was measured using an X-rite SP60 spectrophotometer. Each sample was placed in an ESPEC-SETH-Z-02R damp heat test chamber and tested for 120 hours at a temperature of 50°C and a relative humidity of 95%. Subsequently, the color difference ΔE of the steel plate surface before and after the experiment was measured using a spectrophotometer. The results are shown in Table 4.

[0100] Table 4

[0101] Example 1 92.5 1.45 Example 2 90.6 1.32 Example 3 91.0 1.23 Example 4 91.7 1.04 Example 5 92.1 0.78 Example 6 90.0 0.67 Comparative Example 1 86.6 7.9 Comparative Example 2 72.5 5.8

[0102] Detailed analysis in Table 4:

[0103] The L-value of steel plate surface brightness refers to the brightness of the steel plate surface. The larger the L-value, the brighter and whiter the steel plate surface is, and the more metallic it is.

[0104] The color difference ΔE on the surface of a steel plate refers to the color change of the steel plate surface after wet heat treatment. The smaller the color difference, the stronger the ability of the steel plate coating to resist blackening, and the more stable the metallic luster of the steel plate surface.

[0105] From the data in Examples 1-6, it can be seen that:

[0106] Using the method of this application, a complex layer based on benzotriazole is formed on the surface of the zinc-magnesium-aluminum coating, which can improve the surface blackening resistance of the zinc-magnesium-aluminum coated steel sheet and maintain the metallic luster of the zinc-magnesium-aluminum coated steel sheet. The surface brightness L value of the steel sheet is above 90. Experiments show that the surface color difference ΔE of the steel sheet is below 1.5.

[0107] From the data in Comparative Examples 1-2, we can see that:

[0108] If the method of this application is not adopted, and the zinc-aluminum-magnesium coated steel sheet is directly subjected to chromium-free passivation treatment, the resulting steel sheet has a higher surface color difference ΔE before and after the experiment, indicating that it is not resistant to blackening; or if it is immersed in an aqueous solution containing chloride ions and sulfate ions and then subjected to chromium-free passivation treatment, the resulting steel sheet has a higher ΔE, indicating that it has poor resistance to blackening, and its surface brightness L value is lower, indicating that its surface is dull and has poor metallic luster.

[0109] In summary, the technical solutions provided in the embodiments of this application have the following technical effects and advantages:

[0110] (1) The method provided in this application improves the blackening resistance of the zinc-aluminum-magnesium coating surface under humid heat conditions by forming a complex layer based on benzotriazole on the surface of the zinc-aluminum-magnesium coated steel plate, and the surface color difference ΔE in the humid heat test is less than 1.5.

[0111] (2) The zinc-aluminum-magnesium coated steel sheet provided in this application has a colorless and transparent complex layer based on benzotriazole on its surface, which will not affect the metallic luster of the zinc-aluminum-magnesium coated steel sheet, thereby maintaining the metallic luster of the zinc-aluminum-magnesium coated steel sheet, and the surface brightness L value of the steel sheet is above 90.

[0112] (3) The aqueous solution or passivation solution used in the embodiments of this application does not contain chromium, which is environmentally friendly.

[0113] (4) The zinc-aluminum-magnesium coated steel plate preparation method provided in this application does not require equipment modification of the galvanizing production line, and improves the blackening problem of steel plate and maintains the metallic luster of steel plate at low cost.

[0114] (5) The zinc-aluminum-magnesium coated steel sheet provided in this application embodiment can meet the requirements of high-end home appliance and building users for product appearance.

[0115] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical 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 single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0116] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the orientation shown in the accompanying drawings. Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to."

[0117] In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any actual relationship or order between these entities or operations. In this document, "and / or" describes the association between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0118] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a zinc-aluminum-magnesium coated steel sheet, characterized in that, The method includes: A steel substrate is placed in a plating solution containing a set chemical composition to obtain a zinc-aluminum-magnesium coated steel sheet. Cool the zinc-aluminum-magnesium coated steel sheet to a first set temperature; The soaking solution containing benzotriazole is heated to the second set temperature; The cooled zinc-aluminum-magnesium coated steel sheet is placed in the heated immersion solution and immersed for a set time. The zinc-aluminum-magnesium coated steel sheet after soaking is subjected to chromium-free passivation treatment. The mass concentration of the benzotriazole is 0.5 g / L-1 g / L; The soaking solution further includes at least one of the following: sodium benzoate, sodium dodecylbenzenesulfonate, and methylbenzotriazole; the mass concentration of methylbenzotriazole is 0.05 g / L-0.2 g / L; the mass concentration of sodium benzoate is 1 g / L-5 g / L; and the mass concentration of sodium dodecylbenzenesulfonate is 0.3 g / L-1 g / L. The first set temperature is 120℃-180℃, and the second set temperature is 35℃-60℃; The chemical composition of the plating solution includes: Mg: 0.7 wt%-1.1 wt%, Al: 55 wt%-56 wt%, Si: 1.5 wt%-1.6 wt%, Zn.

2. The preparation method according to claim 1, characterized in that, The set duration is between 1 minute and 10 minutes.

3. A zinc-aluminum-magnesium coated steel sheet, characterized in that, The zinc-aluminum-magnesium coated steel sheet is prepared by the preparation method according to any one of claims 1-2. The zinc-aluminum-magnesium coated steel sheet includes a steel substrate, a zinc-aluminum-magnesium coating covering the surface of the steel substrate, a benzotriazole-based complex layer covering the surface of the zinc-aluminum-magnesium coating, and a chromium-free passivation layer covering the surface of the benzotriazole-based complex layer.

4. The zinc-aluminum-magnesium coated steel sheet according to claim 3, characterized in that, The chemical composition of the zinc-aluminum-magnesium coating includes: Mg: 0.7 wt%-1.1 wt%, Al: 55 wt%-56 wt%, Si: 1.5 wt%-1.6 wt%, Zn.

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