Zinc-aluminum-magnesium plated layer, zinc-aluminum-magnesium plated steel sheet, and method for producing the same

Abstract

The application relates to a zinc-aluminum-magnesium coating, a zinc-aluminum-magnesium coated steel plate and a preparation method thereof, the chemical composition of the zinc-aluminum-magnesium coating comprises Mg, Al, Fe, Ni and Zn; wherein the content of Mg is 1.6% to 3% in terms of mass fraction, the content of Al is 2.5% to 4% in terms of mass fraction, the content of Fe is 3% to 8% in terms of mass fraction, and the content of Ni is 0.1% to 1% in terms of mass fraction; wherein 50% to 90% of the Ni is distributed in a depth range of 3 mu m below the surface of the zinc-aluminum-magnesium coating; and the inside and the surface of the zinc-aluminum-magnesium coating both contain 5% to 40% of Fe-Zn compounds. The application improves the filamentous corrosion resistance of the zinc-aluminum-magnesium coating.

Description

Technical Field

[0001] This application relates to the field of steel preparation 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] Zinc-aluminum-magnesium coated steel sheet is a new type of high corrosion-resistant alloy coated steel sheet. This coating was developed based on the traditional pure zinc coating, with the addition of magnesium and aluminum elements, which significantly improves the corrosion resistance of the coating on both the surface and the cut edges. It can be widely used in the manufacture of automobiles, home appliances, building exterior walls, etc.

[0003] In the automotive and home appliance industries, zinc-aluminum-magnesium (ZAM) coated steel sheets are typically used after painting. Painting involves applying an organic film to the surface of the steel sheet coating, including electrophoretic coatings, primers, and topcoats. However, due to the presence of highly electrochemically active magnesium (Mg) in the ZAM coating, filamentous corrosion can occur under certain conditions, forming corrosion morphologies that extend in specific directions. This filamentous corrosion affects the appearance quality of the organic film and, in severe cases, can even compromise the coating's corrosion resistance. Summary of the Invention

[0004] This application provides a zinc-aluminum-magnesium coating, a zinc-aluminum-magnesium coated steel plate, and a method for preparing the same, to solve the following technical problem: how to improve the resistance of zinc-aluminum-magnesium coating to filamentous corrosion.

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

[0006] Mg, Al, Fe, Ni, and Zn; wherein, by mass fraction,

[0007] The content of Mg is 1.6%–3%, the content of Al is 2.5%–4%, the content of Fe is 3%–8%, and the content of Ni is 0.1%–1%.

[0008] Of which, 50% to 90% of the Ni is distributed within a depth of 3 μm below the surface of the zinc-aluminum-magnesium coating;

[0009] The zinc-aluminum-magnesium coating contains 5% to 40% Fe-Zn compounds both inside and on the surface.

[0010] Optionally, in the zinc-aluminum-magnesium coating, the content of Mg is 2.5% and the content of Al is 3.7%.

[0011] Optionally, in the zinc-aluminum-magnesium coating, the content of Mg and the content of Al satisfy the following relationship:

[0012] -0.2≤[Mg]¹-[Al]¹*0.7≤0.2

[0013] In the formula, [Mg]1 represents the mass fraction of Mg in the coating, and [Al]1 represents the mass fraction of Al in the coating.

[0014] Optionally, the Fe-Zn compound includes at least one of the following phases: δ1p phase (FeZn10), δ1k phase (FeZn7), Γ1 phase (Fe3Zn10), Γ1 phase (Fe11Zn40), and ξ phase (FeZn13).

[0015] 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 the first aspect, which is attached to at least a portion of the surface of the steel substrate.

[0016] Thirdly, this application provides a method for preparing the zinc-aluminum-magnesium coated steel sheet described in the second aspect, the method comprising:

[0017] The steel substrate is hot-dip galvanized with aluminum-magnesium using a plating solution, and then rolled to obtain the first zinc-aluminum-magnesium coated steel sheet.

[0018] Ni is deposited on at least a portion of the surface of the first zinc-aluminum-magnesium coated steel sheet, followed by heat treatment to allow the Ni and Fe in the steel substrate to diffuse into the zinc-aluminum-magnesium coating of the first zinc-aluminum-magnesium coated steel sheet, thereby obtaining the zinc-aluminum-magnesium coated steel sheet.

[0019] Optionally, the content of Mg and the content of Al in the plating solution satisfy the following relationship:

[0020] -1.5≤[Mg]2-[Al]2*0.7≤0

[0021] In the formula, [Mg]2 represents the mass fraction of Mg in the plating solution, and [Al]2 represents the mass fraction of Al in the plating solution.

[0022] Optionally, the Mg content of the plating solution and the Mg content of the zinc-aluminum-magnesium coating satisfy the following relationship:

[0023] 1% ≤ [Mg]2- [Mg]1 ≤ 4%

[0024] The Al content of the plating solution and the Al content of the zinc-aluminum-magnesium coating satisfy the following relationship:

[0025] 1% ≤ [Al]2 - [Al]1 ≤ 4%

[0026] In the formula, [Mg]1 represents the mass fraction of Mg in the coating, [Al]1 represents the mass fraction of Al in the coating, [Mg]2 represents the mass fraction of Mg in the plating solution, and [Al]2 represents the mass fraction of Al in the plating solution.

[0027] Optionally, the thickness of the deposited Ni is 30 nm to 200 nm.

[0028] Optionally, the heat treatment includes a heating section and a cooling section; wherein the cooling rate of the cooling section is not less than 10 K / s;

[0029] The final temperature of the heating section is 200℃~400℃, and the holding time at the final temperature is 20s~50s.

[0030] The heating rate of the heating section is not less than 10K / s.

[0031] The technical solutions provided in this application have the following advantages compared with the prior art:

[0032] The zinc-aluminum-magnesium coating provided in this application embodiment has the following chemical composition: Mg, Al, Fe, Ni, and Zn; wherein, by mass fraction, the content of Mg is 1.6% to 3%, the content of Al is 2.5% to 4%, the content of Fe is 3% to 8%, and the content of Ni is 0.1% to 1%; wherein, 50% to 90% of the Ni is distributed within a depth range of 3 μm below the surface of the zinc-aluminum-magnesium coating; the interior and surface of the zinc-aluminum-magnesium coating contain 5% to 40% Fe-Zn compounds. Adding Mg and Al to zinc coatings can provide high-quality atmospheric corrosion resistance. With Mg content of 1.6%–3% and Al content of 2.5%–4%, the eutectic content on the zinc-aluminum-magnesium (ZAM) coating surface can be significantly increased. This prevents insufficient eutectic content from causing corrosion to be confined to grain boundaries and eventually extend along the grain boundaries to form filamentous corrosion morphology. Furthermore, with Ni content of 0.1%–1%, Ni combines with Al to form Ni-Al compounds, refining the coating grains and segmenting the Mg-Zn compounds. The fine grain size slows down the dissolution rate of Mg-Zn compounds, thus reducing the rate of filamentous corrosion. 50%–90% of the Ni is distributed within a 3 μm depth below the surface of the zinc-aluminum-magnesium coating, effectively suppressing filamentous corrosion on the coating surface. Furthermore, the 3%–8% Fe content allows Fe and Zn to form Fe-Zn compounds, inhibiting localized rapid corrosion of the eutectic structure and thus suppressing filamentous corrosion. The zinc-aluminum-magnesium coating contains 5%–40% Fe-Zn compounds both internally and on the surface, further inhibiting filamentous corrosion. In summary, this improves the resistance of the zinc-aluminum-magnesium coating to filamentous corrosion. Attached Figure Description

[0033] 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.

[0034] 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.

[0035] Figure 1 The image shows the surface microstructure of a zinc-aluminum-magnesium coated steel sheet according to some embodiments of this application.

[0036] Figure 2 This is a schematic flowchart illustrating a method for preparing a zinc-aluminum-magnesium coated steel sheet according to some embodiments of this application. Detailed Implementation

[0037] 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.

[0038] 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.

[0039] In this application, the terms "comprising," "including," etc., mean "including but not limited to." Relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. 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 multiple 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 each be single or multiple.

[0040] 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.

[0041] Firstly, this application provides a zinc-aluminum-magnesium coating. Figure 1 The image shows the surface microstructure of a zinc-aluminum-magnesium coated steel sheet according to some embodiments of this application; please refer to [link to relevant documentation]. Figure 1 The chemical composition of the zinc-aluminum-magnesium coating includes:

[0042] Mg, Al, Fe, Ni, and Zn; wherein, by mass fraction,

[0043] The content of Mg is 1.6%–3%, the content of Al is 2.5%–4%, the content of Fe is 3%–8%, and the content of Ni is 0.1%–1%.

[0044] Of which, 50% to 90% of the Ni is distributed within a depth of 3 μm below the surface of the zinc-aluminum-magnesium coating;

[0045] The zinc-aluminum-magnesium coating contains 5% to 40% Fe-Zn compounds both inside and on the surface.

[0046] In some embodiments, the zinc-aluminum-magnesium coating contains 2.5% Mg and 3.7% Al.

[0047] In the embodiments of this application, the Al element in the coating provides the coating with high-quality atmospheric corrosion resistance because, during the corrosion process, Al can form dense oxides and dense hydroxides on the surface. If there is too little Al in the coating, the adhesion between the coating and the steel plate will be poor, rendering the coating unusable and reducing corrosion resistance.

[0048] The Mg element in the coating can significantly improve the coating's resistance to atmospheric corrosion. The mechanism is that the Mg in the coating will preferentially dissolve into the water film on the coating surface in the atmospheric environment. In the water film, it will react with dissolved carbon dioxide to precipitate a dense protective film. This protective film can exist stably in neutral and weakly alkaline environments. At the same time, it can also promote the electrolyte solution on the coating surface to become a weakly alkaline solution, thereby improving the corrosion resistance of the coating.

[0049] In the atmosphere, especially in high-humidity environments, a thin liquid film adheres to the surface of zinc-aluminum-magnesium coatings. The oxygen enriched in this film preferentially reacts with the magnesium in the coating, rapidly forming magnesium compounds, while the pH value of the liquid film gradually increases. Under these conditions, the liquid film also allows Al to dissolve. This leads to the reaction of the aluminum-rich phase in the coating with oxygen, hydroxide, and carbonate ions in the liquid film, forming complex aluminum-rich compounds.

[0050] Zinc-aluminum-magnesium (ZAM) coatings often form large initial solidification structures as well as fine eutectic structures. The eutectic structure typically consists of Mg-Zn compounds, aluminum-rich phases, and zinc-rich phases. The eutectic structure in ZAM coatings preferentially leads to localized corrosion. If the eutectic structure on the ZAM coating surface is sparse, this corrosion will be confined to the vicinity of the grain boundaries. With an organic film applied to the coating surface, localized corrosion can extend along the grain boundaries, forming filamentary corrosion morphologies.

[0051] Therefore, by appropriately adjusting the Al and Mg content in the zinc-aluminum-magnesium coating to significantly increase the proportion of eutectic structure in the coating, the eutectic structure can form clusters, thereby avoiding the formation of filamentous corrosion. For example, the Mg content can be 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, etc., and the Al content can be 2.5%, 2.7%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, etc. Furthermore, when the Al content in the zinc-aluminum-magnesium coating is 3.7% and the Mg content is 2.5%, the coating is almost entirely composed of eutectic structure. This eutectic structure can contain fine ternary eutectic structures, which can make the anodic active sites and cathodic active sites of localized corrosion closer together, thus making it less likely for localized corrosion to spread into filamentous corrosion morphology.

[0052] Furthermore, with a Ni content of 0.1% to 1%, Ni combines with Al to form Ni-Al compounds, refining the grain size of the coating and dividing the Mg-Zn compounds into fine grains, thus slowing down the dissolution rate of the Mg-Zn compounds and reducing the rate of filamentous corrosion. 50% to 90% of the Ni is distributed within a 3μm depth range below the surface of the zinc-aluminum-magnesium coating, effectively suppressing filamentous corrosion on the coating surface. However, excessively high Ni content can lead to a significant galvanic reaction with the magnesium in the coating, resulting in a decrease in the corrosion resistance of the zinc-aluminum-magnesium coating. For example, the Ni content can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc., and the Ni content distributed within a 3μm depth range below the surface of the zinc-aluminum-magnesium coating can be 50%, 60%, 70%, 80%, 90%, etc. The distribution range of nickel in the coating can be determined using glow discharge spectroscopy. When testing the Ni content, a current of 20 mA and an anode diameter of 4 mm are used for the glow discharge spectroscopy.

[0053] With an Fe content of 3%–8%, Fe and Zn form Fe-Zn compounds, which can inhibit localized rapid corrosion of the eutectic structure, thereby suppressing filamentary corrosion. The zinc-aluminum-magnesium coating contains 5%–40% Fe-Zn compounds both internally and on the surface, effectively suppressing filamentary corrosion on the coating surface. The distribution of Fe-Zn compounds in the coating may be uneven. There will be some difference in the Fe-Zn compound content between the coating surface and the coating interior. However, filamentary corrosion mainly occurs on the coating surface. Therefore, the Fe-Zn compound content is limited both internally and on the surface of the zinc-aluminum-magnesium coating. For example, the Fe content can be 3%, 4%, 5%, 6%, 7%, 8%, etc.; the Fe-Zn compound content contained in the internal and surface of the zinc-aluminum-magnesium coating can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc.

[0054] In some embodiments, the content of Mg and the content of Al in the zinc-aluminum-magnesium coating satisfy the following relationship:

[0055] -0.2≤[Mg]¹-[Al]¹*0.7≤0.2

[0056] In the formula, [Mg]1 represents the mass fraction of Mg in the coating, and [Al]1 represents the mass fraction of Al in the coating.

[0057] In the embodiments of this application, the eutectic structure may include fine ternary eutectic structures, which can make the anodic active sites and cathodic active sites of localized corrosion closer together, thereby making it less likely for localized corrosion to expand into filamentous corrosion morphology. Satisfying -0.2≤[Mg]1-[Al]1*0.7≤0.2 ensures that the eutectic structure in the coating is mainly a ternary eutectic structure.

[0058] In some embodiments, the Fe-Zn compound comprises at least one of the following phases: δ1p phase (FeZn10), δ1k phase (FeZn7), Γ1 phase (Fe3Zn10), Γ1 phase (Fe11Zn40), and ξ phase (FeZn13).

[0059] In the embodiments of this application, the phase in the Fe-Zn compound can be one or more of the following: δ1p phase (FeZn10), δ1k phase (FeZn7), Γ1 phase (Fe3Zn10), Γ1 phase (Fe11Zn40), and ξ phase (FeZn13).

[0060] 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 the first aspect, which is attached to at least a portion of the surface of the steel substrate.

[0061] In this embodiment, the steel substrate is not specifically limited; ordinary steel plates such as hot-rolled steel plates and cold-rolled steel plates can be used. The type of steel is also not specifically limited; for example, aluminum-killed steel, ultra-low carbon steel, and high-strength steel can be used. Through the above-mentioned design of the coating alloy composition and the chemical composition of the coating surface, the resistance to filamentous corrosion of the zinc-aluminum-magnesium coating can be significantly improved, thereby giving the zinc-aluminum-magnesium coated steel plate good resistance to filamentous corrosion.

[0062] The zinc-aluminum-magnesium coated steel sheet is based on the above-mentioned zinc-aluminum-magnesium coating. The specific chemical composition of the zinc-aluminum-magnesium coating can be referred to the above embodiments. Since the 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.

[0063] Thirdly, this application provides a method for preparing the zinc-aluminum-magnesium coated steel sheet described in the second aspect. Figure 2 For a flowchart illustrating a method for preparing a zinc-aluminum-magnesium coated steel sheet according to some embodiments of this application, please refer to [link / reference]. Figure 2 The method includes:

[0064] S1. The steel substrate is hot-dip galvanized with aluminum-magnesium using a plating solution, and then rolled to obtain the first zinc-aluminum-magnesium coated steel sheet.

[0065] S2. Ni is deposited on at least a portion of the surface of the first zinc-aluminum-magnesium coated steel sheet, followed by heat treatment, so that the Ni and Fe in the steel substrate diffuse into the zinc-aluminum-magnesium coating of the first zinc-aluminum-magnesium coated steel sheet, thereby obtaining the zinc-aluminum-magnesium coated steel sheet.

[0066] In some embodiments, the content of Mg and the content of Al in the plating solution satisfy the following relationship:

[0067] -1.5≤[Mg]2-[Al]2*0.7≤0

[0068] In the formula, [Mg]2 represents the mass fraction of Mg in the plating solution, and [Al]2 represents the mass fraction of Al in the plating solution.

[0069] In some embodiments, the Mg content of the plating solution and the Mg content of the zinc-aluminum-magnesium coating satisfy the following relationship:

[0070] 1% ≤ [Mg]2- [Mg]1 ≤ 4%

[0071] The Al content of the plating solution and the Al content of the zinc-aluminum-magnesium coating satisfy the following relationship:

[0072] 1% ≤ [Al]2 - [Al]1 ≤ 4%

[0073] In the formula, [Mg]1 represents the mass fraction of Mg in the coating, [Al]1 represents the mass fraction of Al in the coating, [Mg]2 represents the mass fraction of Mg in the plating solution, and [Al]2 represents the mass fraction of Al in the plating solution.

[0074] In this embodiment, continuous hot-dip galvanizing can more easily produce zinc-aluminum-magnesium coated steel sheets, while the coating exhibits good density and uniform microstructure. The Al and Mg content in the continuous hot-dip galvanizing solution is required to be higher than the Al and Mg content in the coating. This is because Fe and Ni atoms are added to the coating in step S3. Therefore, the Mg content in the galvanizing solution is adjusted to satisfy -1.5 ≤ [Mg]² - [Al]² * 0.7 ≤ 0; the Mg content in the galvanizing solution and the Mg content in the zinc-aluminum-magnesium coating satisfy the following relationship: 1% ≤ [Mg]² - [Mg]¹ ≤ 4%; the Al content in the galvanizing solution and the Al content in the zinc-aluminum-magnesium coating satisfy the following relationship: 1% ≤ [Al]² - [Al]¹ ≤ 4%.

[0075] In some embodiments, the thickness of the deposited Ni is 30 nm to 200 nm.

[0076] In this embodiment, after the zinc-aluminum-magnesium alloy coating is applied, rolling is performed to activate the surface state of the first zinc-aluminum-magnesium coated steel plate, facilitating the deposition of nickel on the coating surface and introducing nickel into the zinc-aluminum-magnesium coating. To achieve the desired nickel content in the coating, the thickness of the deposited nickel layer is limited. For example, the thickness of the deposited Ni can be 30nm, 50nm, 70nm, 90nm, 100nm, 120nm, 140nm, 160nm, 180nm, 200nm, etc.

[0077] In some embodiments, the heat treatment includes a heating section and a cooling section; wherein the cooling rate of the cooling section is not less than 10 K / s;

[0078] The final temperature of the heating section is 200℃~400℃, and the holding time at the final temperature is 20s~50s.

[0079] The heating rate of the heating section is not less than 10K / s.

[0080] In this embodiment, the heat treatment serves to diffuse Fe atoms from the steel plate into the coating, forming Fe-Zn compounds, and simultaneously allow Ni atoms deposited on the surface to diffuse into the coating, enriching it on the surface and combining with Al in the coating. Atom diffusion requires a certain amount of time and temperature. If the final temperature of the heating stage is too low or the holding time is too short, the diffusion effect cannot be achieved, resulting in too low Fe content and a too low proportion of Fe-Zn compounds in the coating. Furthermore, the deposited Ni cannot diffuse into the coating, causing excessive Ni distribution within a 3-micrometer depth below the coating surface. The heating and cooling processes should achieve relatively fast heating and cooling rates so that the heating and cooling processes do not significantly affect the coating performance. For example, the cooling rate of the cooling section is 10K / s, 11K / s, 12K / s, 13K / s, 14K / s, 15K / s, etc., the final temperature of the heating section can be 200℃, 230℃, 250℃, 270℃, 300℃, 330℃, 350℃, 370℃, 400℃, etc., the holding time under the above final temperature conditions can be 20s, 25s, 30s, 35s, 40s, 45s, 50s, etc., and the heating rate of the heating section can be 10K / s, 11K / s, 12K / s, 13K / s, 14K / s, 15K / s, etc.

[0081] The preparation method of the zinc-aluminum-magnesium coated steel sheet is based on the above-mentioned zinc-aluminum-magnesium coated steel sheet. The specific structure of the zinc-aluminum-magnesium coating can be referred to the above embodiments. Since the preparation method of the 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.

[0082] 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.

[0083] This application provides a zinc-aluminum-magnesium coating, the characteristics of which are shown in Table 1.

[0084] Table 1 Characteristics of Zinc-Aluminum-Magnesium Coatings

[0085]

[0086]

[0087] This application provides a zinc-aluminum-magnesium coated steel sheet and its preparation method. A steel sheet with a thickness of 1.0 mm and a width of 1000 mm is used as the substrate, and the coating weight is 100 grams per square meter on both sides. The preparation process parameters for this zinc-aluminum-magnesium coated steel sheet are shown in Table 2.

[0088] Table 2. Manufacturing process parameters for zinc-aluminum-magnesium coated steel sheets

[0089]

[0090]

[0091]

[0092] Filament corrosion resistance assessment test: The zinc-aluminum-magnesium coated steel sheets obtained according to Examples 1-13 and Comparative Examples 1-10 above were subjected to filament corrosion resistance assessment test.

[0093] A 20-micron-thick PVB organic film was coated on the zinc-aluminum-magnesium plating surface. Then, scratches were made on the surface of the organic film, with a scratch width of 1 mm and a scratch depth reaching the steel substrate. 5 μL of acetic acid solution with a concentration of 1 mol / dm³ was injected into the scratched areas. 3 The samples were then placed in a constant temperature and humidity environment (22℃, 86% RH) and stored for 4 weeks. The growth length of filamentary corrosion on the sample surface was then evaluated according to GB / T 30789.9. Longer growth indicates a greater susceptibility to filamentary corrosion. Table 3 shows the experimental results of the resistance to filamentary corrosion of zinc-aluminum-magnesium coated steel sheets.

[0094] Corrosion resistance test: The zinc-aluminum-magnesium coated steel sheets obtained according to Examples 1-13 and Comparative Examples 1-10 above were evaluated for corrosion resistance.

[0095] The corrosion evaluation method involves placing the galvanized steel sheet in a cyclic corrosion test chamber and conducting 10 cycles of cyclic corrosion testing. The cyclic corrosion test must meet the requirements of Annex A of ISO 1:1997-1:2017. Then, the mass loss of the coating before and after the test is measured, and the corrosion resistance of the coating is evaluated using the mass loss per unit area. The less the mass loss, the better the corrosion resistance. Table 3 shows the experimental results of the corrosion resistance evaluation of zinc-aluminum-magnesium coated steel sheets.

[0096] Table 3. Experimental Results of Zinc-Aluminum-Magnesium Coated Steel Sheets' Resistance to Filament Corrosion and Corrosion Evaluation

[0097]

[0098]

[0099] As shown in Table 3, the zinc-aluminum-magnesium coating surface of the present application embodiment has excellent resistance to filamentous corrosion, and thus the zinc-aluminum-magnesium coated steel plate surface has excellent resistance to filamentous corrosion, while also taking into account corrosion resistance.

[0100] 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: Mg, Al, Fe, Ni, and Zn; wherein, by mass fraction, The content of Mg is 1.6%~3%, the content of Al is 2.5%~4%, the content of Fe is 3%~8%, and the content of Ni is 0.1%~1%. Of which, 50% to 90% of the Ni is distributed within a depth of 3 μm below the surface of the zinc-aluminum-magnesium coating; The zinc-aluminum-magnesium coating contains 5% to 40% Fe-Zn compounds both inside and on the surface. In the zinc-aluminum-magnesium coating, the content of Mg and the content of Al satisfy the following relationship: -0.2≤[Mg]¹-[Al]¹*0.7≤0.2 In the formula, [Mg]1 represents the mass fraction of Mg in the coating, and [Al]1 represents the mass fraction of Al in the coating.

2. The zinc-aluminum-magnesium coating according to claim 1, characterized in that, In the zinc-aluminum-magnesium coating, the content of Mg is 2.5% and the content of Al is 3.7%.

3. The zinc-aluminum-magnesium coating according to claim 1, characterized in that, The Fe-Zn compound comprises at least one of the following phases: FeZn 10 δ 1p Phase, FeZn7δ 1k Phase, Fe3Zn 10 Γ1 phase, Fe 11 Zn 40 Γ1 phase, FeZn 13 ξ phase.

4. A zinc-aluminum-magnesium coated steel sheet, characterized in that, The zinc-aluminum-magnesium coated steel sheet includes a steel substrate and a zinc-aluminum-magnesium coating as described in any one of claims 1 to 3, which is attached to at least a portion of the surface of the steel substrate.

5. A method for preparing the zinc-aluminum-magnesium coated steel sheet according to claim 4, characterized in that, The method includes: The steel substrate is hot-dip galvanized with aluminum-magnesium using a plating solution, and then rolled to obtain the first zinc-aluminum-magnesium coated steel sheet. Ni is deposited on at least a portion of the surface of the first zinc-aluminum-magnesium coated steel sheet, followed by heat treatment to allow the Ni and Fe in the steel substrate to diffuse into the zinc-aluminum-magnesium coating of the first zinc-aluminum-magnesium coated steel sheet, thereby obtaining the zinc-aluminum-magnesium coated steel sheet.

6. The method according to claim 5, characterized in that, In the plating solution, the content of Mg is related to that of Al. The content of satisfies the following relationship: -1.5≤[Mg]2-[Al]2*0.7≤0 In the formula, [Mg]2 represents the mass fraction of Mg in the plating solution, and [Al]2 represents the mass fraction of Al in the plating solution.

7. The method according to claim 5, characterized in that, The Mg content of the plating solution is related to the zinc, aluminum, and magnesium content. The Mg content in the coating satisfies the following relationship: 1%≤[Mg]2-[Mg]1≤4% The Al content of the plating solution and the Al content of the zinc-aluminum-magnesium coating satisfy the following relationship: 1%≤[Al]2-[Al]1≤4% In the formula, [Mg]1 represents the mass fraction of Mg in the coating, [Al]1 represents the mass fraction of Al in the coating, [Mg]2 represents the mass fraction of Mg in the plating solution, and [Al]2 represents the mass fraction of Al in the plating solution.

8. The method according to claim 5, characterized in that, The thickness of the deposited Ni is 30 nm to 200 nm.

9. The method according to claim 5, characterized in that, The heat treatment includes a heating section and a cooling section; wherein the cooling rate of the cooling section is not less than 10 K / s; The final temperature of the heating section is 200℃~400℃, and the holding time at the final temperature is 20s~50s. The heating rate of the heating section is not less than 10K / s.

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