A zinc-aluminum-magnesium coating, a zinc-aluminum-magnesium coated steel plate and its preparation method

Abstract

This application relates to a zinc-aluminum-magnesium coating, a zinc-aluminum-magnesium coated steel sheet, and a method for preparing the same. The chemical composition of the zinc-aluminum-magnesium coating includes Al, Mg, Mn, and Zn; wherein the weight content of Mn is 0.5-5%, and the weight ratio of Mn to Al is ≥0.5. The zinc-aluminum-magnesium coating contains Al8Mn5 phase precipitated at grain boundaries, and hexagonal Al phase precipitated simultaneously at grain boundaries and in the pure zinc phase. 0.8 The precipitation of Mn phases refines the microstructure, and the solid solution formed by Mn dissolving in the matrix reduces the potential difference between the intermetallic compound and the matrix, thereby improving the corrosion resistance of the matrix. This gives zinc-aluminum-magnesium coated steel sheets excellent corrosion resistance.

Description

Technical Field

[0001] This application relates to the field of coating technology, and in particular to a zinc-aluminum-magnesium coating, a zinc-aluminum-magnesium coated steel plate, and a method for preparing the same. Background Technology

[0002] Hot-dip galvanizing is one of the important methods to improve the corrosion resistance of steel plates. Zn-Al-Mg galvanized coatings have attracted increasing attention due to their excellent corrosion resistance, especially at cutting edges. Furthermore, the microhardness and scratch resistance of Zn-Al-Mg alloy coatings surpass those of other alloy coatings. However, the corrosion resistance of traditional Zn-Al-Mg coatings still falls short of meeting the needs of many users.

[0003] Therefore, there is an urgent need to further improve the corrosion resistance of traditional Zn-Al-Mg coatings. Summary of the Invention

[0004] This application provides a zinc-aluminum-magnesium coating, a zinc-aluminum-magnesium coated steel sheet, and a method for preparing the same, in order to solve the technical problem of insufficient corrosion resistance of existing zinc-aluminum-magnesium coated steel sheets.

[0005] In a first aspect, this application provides a zinc-aluminum-magnesium coating, the chemical composition of which includes:

[0006] Al, Mg, Mn, and Zn; among them,

[0007] The weight content of Mn is 0.5% to 5%, and the ratio of the weight content of Mn to the weight content of Al is ≥0.5.

[0008] Optionally, the Mg content is 0.8-3% by weight, and the Al content is 0.8-3% by weight;

[0009] Furthermore, the weight ratio of Al to Mg is ≤3.

[0010] Optionally, the Al on the surface of the zinc-aluminum-magnesium coating 0.8 The volume fraction of the Mn compound is ≥10%.

[0011] Optionally, the microstructure of the zinc-aluminum-magnesium coating includes a eutectic structure, and the area fraction of the eutectic structure is ≥25%.

[0012] Optionally, the microstructure of the zinc-aluminum-magnesium coating includes a pure zinc phase structure, wherein the grain size of the pure zinc phase structure is <50μm.

[0013] Secondly, this application provides a zinc-aluminum-magnesium coated steel sheet, the zinc-aluminum-magnesium coated steel sheet comprising a steel substrate and a zinc-aluminum-magnesium coating as described in any one embodiment of the first aspect attached to at least a portion of the surface of the steel substrate.

[0014] Thirdly, this application provides a method for preparing the zinc-aluminum-magnesium coated steel sheet according to any embodiment of the second aspect, the method comprising:

[0015] The steel plate is annealed, and the annealing temperature is controlled to obtain a steel matrix;

[0016] The steel substrate is hot-dip coated with a zinc-aluminum-magnesium molten solution, and the temperature of the zinc-aluminum-magnesium molten solution is controlled to obtain a zinc-aluminum-magnesium coated steel sheet.

[0017] Optionally, the temperature of the zinc-aluminum-magnesium melt is 460–560°C.

[0018] Optionally, the hot-dip coating time is 50 to 70 seconds.

[0019] Optionally, the annealing temperature is 720–740°C.

[0020] The technical solutions provided in this application have the following advantages compared with the prior art:

[0021] The zinc-aluminum-magnesium coating provided in this application embodiment, based on the traditional Zn, Al, Mg ternary alloy, incorporates Mn in the coating, resulting in the precipitation of hexagonal Al crystals. 0.8 Mn is dispersed throughout pure zinc, thus contributing to improved corrosion resistance of the coating. Furthermore, since manganese has a relatively higher electrochemical potential than zinc, Mn-containing zinc-aluminum-magnesium coatings exhibit better corrosion resistance than traditional zinc-aluminum-magnesium coatings. Attached Figure Description

[0022] 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.

[0023] 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.

[0024] Figure 1 A microstructure diagram of a zinc-aluminum-magnesium coating provided in an embodiment of this application;

[0025] Figure 2 This application provides a method for preparing a zinc-aluminum-magnesium coating.

[0026] Figure 3 A comparison of electrochemical curves of zinc-aluminum-magnesium coatings in Example 1 and Comparative Example 3, provided as embodiments of this application. Detailed Implementation

[0027] 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.

[0028] 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.

[0029] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely 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. In this document, "and / or" describes the relationship 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 one" 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 mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0030] 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.

[0031] Firstly, this application provides a zinc-aluminum-magnesium coating, please refer to [link to relevant documentation]. Figure 1 The chemical composition of the zinc-aluminum-magnesium coating includes:

[0032] Al, Mg, Mn, and Zn; among them,

[0033] The weight content of Mn is 0.5% to 5%, and the ratio of the weight content of Mn to the weight content of Al is ≥0.5.

[0034] In the embodiments of this application, manganese is the third largest transition element and a desulfurizer, which also improves the strength and toughness of steel. Manganese is electrochemically more negative than zinc and iron. Therefore, like Zn, Mn can provide sacrificial protection for iron and steel. The addition of manganese has been shown to successfully improve the corrosion resistance of coatings developed by electrodeposition and PVD processes, with the beneficial effect of manganese on improving the performance of zinc-plated layers confirmed. Zn-Mn coatings exhibit better corrosion resistance than Zn coatings, attributed to the relatively higher electrochemical potential of manganese compared to the negative electrochemical potential of zinc. When manganese dissolves in the matrix to form a solid solution, it reduces the potential difference between the intermetallic compound and the matrix, thereby improving the corrosion resistance of the matrix. With the addition of Mn content, the compounds formed at room temperature are Al8Mn5 and Al... 0.8 The melting point and precipitation temperature of each phase in the Mn alloy tend to increase. Therefore, the Zn-Al-Mg coating with added Mn exhibits better corrosion resistance than the Zn-Al-Mg coating. When the mass percentage of Mn is too high, elemental Mn will be formed. Corrosion resistance decreases with increasing Mn content. Conversely, when the Mn content is too low, Al-Mn phase precipitation cannot be observed in the alloy microstructure. Specifically, the weight content of Mn can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 4.5%, 5.0%, etc.

[0035] Furthermore, when the Mn content is low, and the ratio of Mn to Al is too low, Mn dissolves in the solid solution. Although solid solution strengthening increases the alloy's strength, the alloy's plasticity and toughness decrease. Moreover, due to the lack of Al-Mn metal compound precipitation, the grains are relatively coarse, and corrosion resistance is not improved. Specifically, the weight ratio of Mn to Al can be 0.5, 0.6, 0.7, 0.8, 1.0, etc.

[0036] In some embodiments, the Mg content is 0.8-3% by weight, and the Al content is 0.8-3% by weight.

[0037] Furthermore, the weight ratio of Al to Mg is ≤3.

[0038] In the embodiments of this application, the addition of Mg can improve the coating quality and reduce zinc consumption. Adding Mg to the Zn-Al alloy can refine the grains, make the coating structure more uniform, and strengthen the grain boundaries. It can also promote the formation of dense and insulating Zn... 5( The addition of Mg inhibits the formation of OH)8Cl2·H2O; suppresses the cathodic reaction; and inhibits the formation of unprotected product ZnO. Mg formation on the alloy coating surface results in MgO, which fills corrosion cracks in the coating, preventing further corrosion and giving the Zn-Mg alloy coating a self-healing function, thus improving its corrosion resistance. Adding Mg to Zn-Al coatings can inhibit the formation of Zn4CO, which offers no protection to the coating. 3( The formation of corrosion products such as Zn(OH)₂·H₂O and ZnO is inhibited. Adding Mg to the coating can suppress the conversion of Zn(OH)₂ to ZnO. In salt spray tests, adding magnesium to the coating promotes the formation of ZnCl₂·Zn(OH)₂. This product can control the diffusion of dissolved oxygen in the liquid, inhibit intergranular corrosion, refine the particles, and make the coating bright. However, when the Mg content is high, it may cause the coating to peel off and flak, and is prone to black rust. Specifically, the weight content of Mg can be 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0039] Al is the most commonly used alloying element in galvanized coatings. Its addition can significantly reduce the corrosion resistance of the galvanized layer. Tests have shown that the corrosion rate of a Zn-5% Al coating is 57.8% that of a pure zinc coating, greatly reducing the corrosion rate. The addition of Al can also improve the fluidity of the zinc bath, reduce coating thickness, decrease zinc consumption, and save costs; it also improves the brightness of the coating. However, excessively high Al content may cause difficulties in the galvanizing process. Specifically, the weight content of Al mentioned above can be 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0040] Furthermore, in Zn-Al-Mg alloys, the corrosion resistance initially increases and then decreases with increasing Mg content, as Mg is relatively reactive and easily oxidized, and the coating structure also changes. Specifically, the weight ratio of Al to Mg can be 3, 2.8, 2.6, 2.4, 2.2, 2, etc.

[0041] In some embodiments, the Al on the surface of the zinc-aluminum-magnesium coating 0.8 The volume fraction of the Mn compound is ≥10%.

[0042] In the embodiments of this application, Al 0.8The Mn phase refines the microstructure, and the solid solution formed by Mn dissolving in the matrix reduces the potential difference between the intermetallic compounds and the matrix, thereby improving the corrosion resistance of the matrix. This results in the excellent corrosion resistance of the zinc-aluminum-magnesium coated steel sheet. Specifically, the Al phase on the surface of the aforementioned zinc-aluminum-magnesium coating... 0.8 The volume fraction of Mn compounds can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, etc.

[0043] In some embodiments, the microstructure of the zinc-aluminum-magnesium coating includes a eutectic structure, the area fraction of which is ≥25%.

[0044] In the embodiments of this application, the eutectic structure in the coating mainly includes binary eutectic structure and ternary eutectic structure. The eutectic structure preferentially corrodes, locally reducing the pH value, thereby protecting the surrounding substrate and improving the overall corrosion resistance. Specifically, the area fraction of the above-mentioned eutectic structure can be 25%, 30%, 35%, 40%, etc.

[0045] In some embodiments, the microstructure of the zinc-aluminum-magnesium coating comprises a pure zinc phase with a grain size of <50 μm.

[0046] In this embodiment, if the pure zinc phase is too large, it will form a corrosion circuit with a large cathode and a small anode, accelerating the corrosion rate. Therefore, the grain size of the pure zinc phase must be controlled to form a circuit with a small cathode and anode, reducing corrosion kinetics and improving the corrosion resistance of the coating. Specifically, the grain size of the pure zinc phase structure can be 48μm, 46μm, 44μm, 42μm, 40μm, etc.

[0047] Secondly, this application provides a zinc-aluminum-magnesium coated steel sheet, the zinc-aluminum-magnesium coated steel sheet comprising a steel substrate and a zinc-aluminum-magnesium coating as described in any one embodiment of the first aspect attached to at least a portion of the surface of the steel substrate.

[0048] In the embodiments of this application, the zinc-aluminum-magnesium coated steel sheet described above has good corrosion resistance.

[0049] Thirdly, this application provides a method for preparing the zinc-aluminum-magnesium coated steel sheet described in any embodiment of the second aspect. Please refer to [link to relevant documentation]. Figure 2 The method includes:

[0050] S1. Anneal the steel plate, controlling the annealing temperature to obtain a steel matrix;

[0051] In some embodiments, the annealing temperature is 720–740°C.

[0052] In this embodiment, a suitable annealing temperature can eliminate the rolling stress on the surface of the steel substrate, remove surface distortion at grain boundaries, make the surface of the steel substrate more uniform, and avoid the formation of locally strong and weak chemically active sites, thus facilitating better subsequent hot-dip galvanizing. Specifically, the annealing temperature can be 720℃, 725℃, 730℃, 735℃, 740℃, etc. Furthermore, to ensure the surface quality of the steel plate, pickling is performed before annealing.

[0053] S2. The steel substrate is hot-dip coated with zinc-aluminum-magnesium molten liquid, and the temperature of the zinc-aluminum-magnesium molten liquid is controlled to obtain a zinc-aluminum-magnesium coated steel sheet.

[0054] In some embodiments, the temperature of the zinc-aluminum-magnesium melt is 460–560°C.

[0055] In some embodiments, the hot-dip coating time is 50 to 70 seconds.

[0056] In this embodiment, a suitable temperature of the zinc-aluminum-magnesium melt ensures sufficient diffusion and dissolution of Mn atoms to guarantee the uniformity of the alloy sample's microstructure; a suitable hot-dip galvanizing time ensures sufficient wetting time. Specifically, the temperature of the zinc-aluminum-magnesium melt can be 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, etc., and the hot-dip galvanizing time can be 50s, 55s, 60s, 65s, 70s, etc.

[0057] The method for preparing zinc-aluminum-magnesium coated steel sheet is based on the above-mentioned aluminum-magnesium coated steel sheet, which can be referred to in the above embodiments. Since the method for preparing zinc-aluminum-magnesium coated steel sheet adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0058] 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.

[0059] This application provides a zinc-aluminum-magnesium coating; for its specific chemical composition and microstructure, please refer to [link to relevant documentation]. Figure 1 .

[0060] Table 1 Chemical composition and microstructure of zinc-aluminum-magnesium coatings

[0061]

[0062] Based on the chemical composition of the zinc-aluminum-magnesium coating described above, this application provides a zinc-aluminum-magnesium coated steel sheet and a method for preparing the same, the method comprising:

[0063] S11. Anneal the steel plate, controlling the annealing temperature to obtain a steel matrix;

[0064] S21. The steel substrate is hot-dip coated with a zinc-aluminum-magnesium molten solution, and the temperature of the zinc-aluminum-magnesium molten solution is controlled to obtain a zinc-aluminum-magnesium coated steel sheet. Specific process parameters are shown in Table 2.

[0065] Table 2. Process parameters for preparing zinc-aluminum-magnesium coated steel sheets

[0066]

[0067]

[0068] Corrosion evaluation was performed on the zinc-aluminum-magnesium coated steel sheets prepared according to the process parameters in Examples 1-5 and Comparative Examples 1-3.

[0069] The corrosion evaluation method involves placing galvanized steel sheets in a cyclic corrosion test chamber and conducting 18 cycles of cyclic corrosion testing, meeting the requirements of Annex A of ISO 1:1997-1:2017. The time it takes for red rust to appear on the alloy surface is then observed; a longer red rust appearance time indicates better corrosion resistance. Simultaneously, Tafel polarization curves are measured. According to electrochemical theory, corrosion potential and corrosion current are the main factors reflecting corrosion resistance. Corrosion potential reflects the trend and probability of the corrosion reaction, while corrosion current reflects the actual process and the kinetics of the corrosion reaction. The results are shown in Table 3.

[0070] Table 3. Corrosion Resistance Test Results of Zinc-Aluminum-Magnesium Coated Steel Sheets

[0071] Example 1 0.223 -1.119 720 Example 2 2.58 -1.025 800 Example 3 4.07 -1.023 840 Example 4 3.59 -1.070 900 Example 5 2.69 -1.117 930 Comparative Example 1 7.13 -0.058 168 Comparative Example 2 18.76 -0.089 150 Comparative Example 3 21.37 -0.069 170

[0072] The corrosion resistance of the high-corrosion-resistant zinc-aluminum-magnesium coated steel sheet and its preparation method described in the embodiments of this application is superior to that of comparative examples 1 to 3.

[0073] In addition, please see Figure 1 The microstructure of the zinc-aluminum-magnesium coating provided in Example 1 shown below, at room temperature, consists of a pure zinc phase and a binary eutectic structure (MgZn2 / Mg2Zn). 11 The composition includes the precipitated phase Al8Mn5, and please refer to [the original text]. Figure 3 The electrochemical curves of the zinc-aluminum-magnesium coatings in Example 1 and Comparative Example 3, as shown in the comparison diagram, indicate that the zinc-aluminum-magnesium coated steel sheet of this application has superior corrosion resistance. The main reason is the precipitation of hexagonal Al crystals. 0.8Mn is dispersed in pure zinc, which helps to improve the corrosion resistance of the coating.

[0074] 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 zinc-aluminum-magnesium coating, characterized in that, The chemical composition of the zinc-aluminum-magnesium coating includes: The zinc-aluminum-magnesium coating contains Al, Mg, Mn, and Zn; wherein the weight content of Mn is 0.5-5%, the weight content of Mg is 0.8-3%, and the weight content of Al is 0.8-3%; and the weight ratio of Al to Mg is ≤3, and the weight ratio of Mn to Al is ≥0.6; the surface of the zinc-aluminum-magnesium coating contains Al. 0.8 The volume fraction of the Mn compound is ≥10%; The microstructure of the zinc-aluminum-magnesium coating includes a eutectic structure and a pure zinc phase structure, wherein the area fraction of the eutectic structure is ≥25% and the grain size of the pure zinc phase structure is <50μm.

2. A zinc-aluminum-magnesium coated steel sheet, characterized in that, The zinc-aluminum-magnesium coated steel sheet includes a steel substrate and the zinc-aluminum-magnesium coating of claim 1, which is attached to at least a portion of the surface of the steel substrate.

3. A method for preparing the zinc-aluminum-magnesium coated steel sheet of claim 2, characterized in that, The method includes: The steel plate is annealed, and the annealing temperature is controlled to obtain a steel matrix; The steel substrate is hot-dip coated with a zinc-aluminum-magnesium molten solution, and the temperature of the zinc-aluminum-magnesium molten solution is controlled to obtain a zinc-aluminum-magnesium coated steel sheet.

4. The method according to claim 3, characterized in that, The temperature of the zinc-aluminum-magnesium melt is 460~560℃.

5. The method according to claim 3, characterized in that, The hot-dip coating time is 50~70s.

6. The method according to claim 3, characterized in that, The annealing temperature is 720~740℃.

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