Filamentous corrosion resistant zinc-aluminum-magnesium coated steel plate and preparation method thereof

Abstract

The invention relates to a filiform corrosion resistant zinc-aluminum-magnesium coated steel plate and a preparation method thereof, and belongs to the technical field of coating. The coated steel plate comprises a steel substrate and a zinc-aluminum-magnesium coating attached to at least part of the surface of the steel substrate, and the zinc-aluminum-magnesium coating comprises the following chemical components in percentage by mass: 1-4% of Mg, 1-4% of Al, 0.1-1% of Sb and a substrate element Zn; and the zinc-aluminum-magnesium plating layer contains an Mg-Sb compound. A proper amount of Sb is added into the plating layer, Sb and Mg react to generate an Mg-Sb compound, on one hand, the Mg-Sb compound consumes part of magnesium, the number of eutectic structure Mg-Zn compounds in the plating layer is reduced, and therefore the sensitivity of filamentous corrosion is reduced; and on the other hand, the Mg-Sb compound also has certain corrosion resistance, so that the overall corrosion resistance of the coating can be further enhanced.

Description

Technical Field

[0001] The present application relates to the field of coating and plating technology, and in particular to a zinc-aluminum-magnesium coated steel plate resistant to filiform corrosion and a preparation method thereof. Background Art

[0002] Hot-dip galvanizing is a process in which steel is immersed in molten zinc liquid to form a zinc-iron alloy layer on the surface of the steel through a chemical reaction. This alloy layer has extremely high adhesion and corrosion resistance, and can effectively protect the steel from corrosion. Hot-dip galvanized steel has the advantages of uniform coating, strong adhesion, long service life, simple manufacturing process and low product price, so it has been widely used in the fields of automobiles and home appliances. In order to further improve the corrosion resistance of hot-dip galvanized coating, especially the protective effect at the cut position of steel plates, people began to add an appropriate amount of Mg to the hot-dip galvanized coating to obtain a zinc-aluminum-magnesium coating. On the basis of retaining the advantages of hot-dip galvanized steel, the zinc-aluminum-magnesium coating can improve the corrosion resistance by more than 20%, and at the same time has the corrosion resistance of the processed cut position.

[0003] However, after adding magnesium to the hot-dip galvanized coating, the zinc-aluminum-magnesium coating will undergo filamentary corrosion under the organic film under certain conditions. Filiform corrosion is a specific corrosion form that expands along a specific direction under the organic film to form a continuous corrosion channel. These corrosion channels often have a long and thin filamentous morphology, hence the name "filamentary corrosion". This corrosion form not only seriously affects the appearance quality of the organic film and reduces the aesthetics of the product, but more importantly, in the process of continuous expansion of the corrosion channel, it will gradually weaken the protective ability of the coating, thereby threatening the corrosion resistance of the entire coating system. Summary of the invention

[0004] The present application provides a zinc-aluminum-magnesium coated steel plate resistant to filiform corrosion and a preparation method thereof, in order to solve the following technical problem: how to improve the filiform corrosion resistance of the zinc-aluminum-magnesium coated steel plate.

[0005] In the first aspect, an embodiment of the present application provides a zinc-aluminum-magnesium coated steel plate resistant to filiform corrosion, wherein the coated steel plate comprises a steel substrate and a zinc-aluminum-magnesium coating attached to at least a portion of the surface of the steel substrate, wherein the chemical composition of the zinc-aluminum-magnesium coating comprises, by mass fraction: Mg: 1% to 4%, Al: 1% to 4%, Sb: 0.1% to 1% and a matrix element Zn; the zinc-aluminum-magnesium coating contains a Mg-Sb compound.

[0006] Optionally, the volume fraction of the Mg—Sb compound is ≥ 0.1%.

[0007] Optionally, the volume fraction of the eutectic structure on the surface of the zinc-aluminum-magnesium coating is ≤20%.

[0008] Optionally, the volume fraction of the eutectic structure on the surface of the zinc-aluminum-magnesium coating is ≥70%.

[0009] Optionally, the chemical composition of the zinc-aluminum-magnesium coating satisfies: [Mg]=(2-10)×[Sb], wherein [Mg] represents the mass fraction of Mg, and [Sb] represents the mass fraction of Sb.

[0010] Optionally, the chemical composition of the zinc-aluminum-magnesium coating satisfies: Al+Mg≤2.5%, wherein Al+Mg represents the sum of the mass fractions of Al and Mg.

[0011] Optionally, the chemical composition of the zinc-aluminum-magnesium coating satisfies: Al+Mg≥5%, wherein Al+Mg represents the sum of the mass fractions of Al and Mg.

[0012] Optionally, the Mg—Sb compound is needle-shaped, and the average length of the Mg—Sb compound is 100 μm to 500 μm.

[0013] In a second aspect, an embodiment of the present application provides a method for preparing the zinc-aluminum-magnesium coated steel sheet resistant to filiform corrosion as described in the first aspect, the method comprising:

[0014] Hot-dip coating the steel substrate to obtain a zinc-aluminum-magnesium coated steel plate;

[0015] The zinc-aluminum-magnesium coated steel sheet is cooled.

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

[0017] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0018] The embodiment of the present application provides a zinc-aluminum-magnesium coated steel plate resistant to filiform corrosion, the coated steel plate 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 comprising, by mass fraction: Mg: 1% to 4%, Al: 1% to 4%, Sb: 0.1% to 1%, and a matrix element Zn; the zinc-aluminum-magnesium coating contains a Mg-Sb compound. By adding an appropriate amount of Sb to the coating, Sb reacts with Mg to form a Mg-Sb compound, which, on the one hand, consumes part of the magnesium, reduces the amount of Mg-Zn compounds in the eutectic structure of the coating, thereby reducing the sensitivity to filiform corrosion; on the other hand, the Mg-Sb compound itself also has certain anti-corrosion properties, which can further enhance the overall corrosion resistance of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0021] Figure 1 A schematic flow chart of a method for preparing a zinc-aluminum-magnesium coated steel plate resistant to filiform corrosion provided in an embodiment of the present application;

[0022] Figure 2 The microstructure diagram provided for Example 7 of the present application;

[0023] Figure 3 This is a microstructure diagram provided for comparative example 2 of the present application. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0025] Various embodiments of the present application may be presented 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 understood as a rigid limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the 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., as well as single 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 in this document, it is meant to include any cited numbers (fractions or integers) within the indicated range.

[0026] In this document, the terms including "including" and "including" mean "including but not limited to". Relational 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 at the same time, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "plurality" 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 all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. "Parts" such as parts by weight and parts by mass indicate the proportional relationship between the components. In the proportional relationship involved in this article, the parameters that need to be described by proportion should be understood as the first term of the proportional formula in the order of description, and the proportional numbers should be understood as the second term of the proportional formula. For example, if the weight ratio of substance A, substance B and substance C is 1:2:3, then substance A, substance B and substance C should correspond to the proportional numbers in the proportional formula in the order of description, that is, the weight of substance A: the weight of substance B: the weight of substance C = 1:2:3.

[0027] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this article can be purchased from the market or prepared by existing methods.

[0028] In the first aspect, an embodiment of the present application provides a zinc-aluminum-magnesium coated steel plate resistant to filiform corrosion, wherein the coated steel plate comprises a steel substrate and a zinc-aluminum-magnesium coating attached to at least a portion of the surface of the steel substrate, wherein the chemical composition of the zinc-aluminum-magnesium coating comprises, by mass fraction: Mg: 1% to 4%, Al: 1% to 4%, Sb: 0.1% to 1%, and a matrix element Zn; the zinc-aluminum-magnesium coating contains a Mg-Sb compound.

[0029] The zinc-aluminum-magnesium coated steel sheet of the embodiment of the present application comprises a steel substrate and a zinc-aluminum-magnesium coating layer attached to at least a portion of the surface of the steel substrate. There is no particular limitation on the steel substrate, and ordinary steel plates such as hot-rolled steel plates and cold-rolled steel plates can be used. There is no particular limitation on the type of steel, and for example, aluminum-killed steel, ultra-low carbon steel, and high-strength steel can be used.

[0030] The Al 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 bonding between the coating and the steel plate will be very poor, resulting in the coating being unusable and reducing corrosion resistance. Exemplarily, the mass fraction of Al in the coating can be: 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc. Mg in the coating can significantly improve the atmospheric corrosion resistance of the coating. The mechanism is that the Mg in the coating will preferentially dissolve into the water film on the surface of the coating in the atmospheric environment, react with dissolved carbon dioxide in the water film, and precipitate a dense protective film. This protective film can exist stably in neutral and weak alkaline environments, and can also cause the electrolyte solution on the surface of the coating to become a weak alkaline solution, thereby improving the corrosion resistance of the coating. Exemplarily, the mass fraction of Mg in the coating can be: 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc.

[0031] If the Al and Mg content in the coating is too low, the corrosion resistance of the coating will be significantly reduced, so the Al and Mg content in the coating is required to be no less than 1%. However, if the Al and Mg content in the coating is too high, more Al-rich FCC phases or Mg-rich HCP phases will appear. Both phases are brittle phases, which can easily cause cracking and peeling of the coating during the deep drawing process of zinc-aluminum-magnesium coated automotive plates. Therefore, the Al and Mg content in the coating should not exceed 4%.

[0032] Adding a certain amount of Sb to the coating can form Mg-Sb compounds with Mg in the coating. The formed Mg-Sb compounds can consume a certain amount of Mg, reduce the Mg-Zn compounds in the eutectic structure, and thus reduce the risk of filamentary corrosion. However, if too much Sb is added, blocky Mg-Sb compounds will be formed in the coating instead of needle-shaped Mg-Sb compounds, which will weaken the effect of the Mg-Sb compounds. At the same time, adding too much Sb will increase the size of the Mg-Sb phase and the proportion of the Mg-Sb compound will be too high, which will increase the brittleness of the coating and make the coating easy to crack and peel off during deep drawing of automobile plates. In addition, too much Sb will cause obvious galvanic corrosion effects in the coating, and the corrosion resistance of the coating will be significantly reduced. Therefore, the addition of Sb is not more than 1%. Exemplarily, the mass fraction of Sb in the coating can be: 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0033] Zn is a matrix element. The specific content / content range of Zn can be obtained by the upper and lower limit formula of the component, that is:

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

[0035] In some embodiments, the chemical composition of the zinc-aluminum-magnesium coating satisfies: [Mg]=(2-10)×[Sb], where [Mg] represents the mass fraction of Mg, and [Sb] represents the mass fraction of Sb.

[0036] The purpose of adding Sb is to obtain Mg-Sb compounds, so there should be a certain relationship between the mass fractions of Mg and Sb so that Mg and Sb can be formed to the maximum extent. Therefore, the amount of Sb added is required to reach one-tenth to one-half of Mg.

[0037] In some embodiments, the volume fraction of the Mg—Sb compound is ≥ 0.1%.

[0038] In some embodiments, the volume fraction of the eutectic structure on the surface of the zinc-aluminum-magnesium coating is ≤20%.

[0039] In some embodiments, the volume fraction of the eutectic structure on the surface of the zinc-aluminum-magnesium coating is ≥70%.

[0040] In the atmosphere, especially in an atmosphere with high humidity, a thin liquid film will adhere to the surface of the zinc-aluminum-magnesium coating. The oxygen enriched in the thin liquid film preferentially reacts electrochemically with the magnesium in the coating to quickly form magnesium compounds, while the pH value in the liquid film gradually increases. In this case, the liquid film can dissolve Al, causing the aluminum-rich phase in the coating to react with the oxygen, hydroxide and carbonate in the liquid film to form aluminum-rich complex compounds.

[0041] Eutectic structure is a special alloy structure, and its formation involves eutectic reaction. Eutectic reaction refers to the process in which a liquid phase simultaneously crystallizes into two solid phases with different compositions and different crystal structures at a certain temperature. The mixture of these two solid phases is collectively referred to as eutectic structure, or eutectic for short. Eutectic structure is divided into ternary eutectic structure and binary eutectic structure. Mg in zinc-aluminum-magnesium coating is mainly concentrated in eutectic structure. The ternary eutectic structure includes aluminum-rich phase, zinc-rich phase and magnesium-zinc compounds, such as Mg 2 Zn 11 MgZn 2Etc. The binary eutectic structure usually only contains magnesium-zinc compounds and zinc-rich phases or aluminum-rich phases. In an acidic environment, the Mg-Zn compounds in the eutectic structure will dissolve preferentially. As the eutectic structure dissolves, the acid ions combine with the magnesium element to form a compound with low solubility and precipitate. If the reaction occurs under the organic film, the location where the acid dissolves and the location where the compound precipitates are not in the same place, and the corrosion presents a filamentary corrosion morphology. In order to inhibit the occurrence of this filamentary corrosion, the most effective way is to eliminate the acidic environment. For the eutectic structure, the zinc-aluminum-magnesium coating is difficult to completely eliminate, because as long as aluminum and magnesium are added, a eutectic structure will be formed. Because the eutectic structure is prone to local corrosion in an acidic environment, it will evolve into filamentary corrosion. Therefore, it is beneficial to reduce the proportion of eutectic structure. The embodiment of the present application can control the proportion of eutectic structure in the coating to less than 20%. For example, the volume fraction of the eutectic structure on the surface of the zinc-aluminum-magnesium coating can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc.

[0042] However, if the content of eutectic structure is high, although the eutectic structure is prone to local corrosion, the local corrosion will not evolve into filiform corrosion, so it is also beneficial to further increase the proportion of eutectic structure. Studies have found that if the proportion of eutectic structure in the coating is not less than 70%, the possibility of filiform corrosion is also low. Exemplarily, the volume fraction of the eutectic structure on the surface of the zinc-aluminum-magnesium coating can be 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, etc.

[0043] In some embodiments, the chemical composition of the zinc-aluminum-magnesium coating satisfies: Al+Mg≤2.5%, where Al+Mg represents the sum of the mass fractions of Al and Mg.

[0044] In order to control the proportion of eutectic structure in the coating to ≤20%, the sum of the contents of Al and Mg in the coating needs to be controlled to ≤2.5%, and of course the contents of Al and Mg cannot be less than 1%. For example, the sum of the mass fractions of Al and Mg in the coating can be 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, etc.

[0045] In some embodiments, the chemical composition of the zinc-aluminum-magnesium coating satisfies: Al+Mg≥5%, where Al+Mg represents the sum of the mass fractions of Al and Mg.

[0046] In order to control the eutectic structure in the coating to ≥70%, the sum of the Al and Mg contents in the coating needs to be controlled to 5% or more, and of course the Al and Mg contents cannot exceed 4%. For example, the sum of the mass fractions of Al and Mg in the coating can be 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, etc.

[0047] In some embodiments, the Mg—Sb compound is needle-shaped, and the average length of the Mg—Sb compound is 100 μm to 500 μm.

[0048] The needle-shaped Mg-Sb compound can penetrate tiny defects or cracks in the coating like a needle, thereby preventing further penetration of corrosive media (such as moisture, oxygen, etc.). When corrosion occurs, these needle-shaped compounds can act as a physical barrier to slow down the expansion of corrosion, especially filamentary corrosion, a form of corrosion that expands along a specific path, so that filamentary corrosion will not have more serious consequences. Further, if the needle-shaped Mg-Sb compound is too short, it cannot serve the purpose of blocking the expansion of filamentary corrosion, so the average length of the Mg-Sb compound in the coating is not less than 100 μm. However, if the Mg-Sb compound is too long, the brittleness of the coating will increase, and the coating will easily crack and peel off during deep drawing of automotive plates, so the average length of the Mg-Sb compound does not exceed 500 μm. Exemplarily, the average length of the Mg-Sb compound can be 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, etc.

[0049] In summary, the embodiments of the present application provide a zinc-aluminum-magnesium coated steel plate resistant to filiform corrosion, which has the following technical advantages:

[0050] This zinc-aluminum-magnesium coated steel plate with filamentary corrosion resistance has a wide range of application prospects in many fields such as construction, automobiles, and home appliances due to its excellent corrosion resistance, hardness, and wear resistance. Especially in environments that require high corrosion resistance, such as seaside and industrial areas, this coated steel plate will show more outstanding performance advantages.

[0051] The zinc-aluminum-magnesium coated steel sheet resistant to filiform corrosion provided in the embodiment of the present application significantly improves the filiform corrosion resistance of the coating by precisely controlling the coating composition and proportion, especially by adding an appropriate amount of Sb to form a Mg-Sb compound. This innovative achievement has brought new breakthroughs in the field of coating technology and also provided related industries with a better quality and high performance material selection.

[0052] Figure 1 A schematic flow chart of a method for preparing a zinc-aluminum-magnesium coated steel plate resistant to filiform corrosion provided in an embodiment of the present application.

[0053] See also Figure 1In a second aspect, an embodiment of the present application provides a method for preparing the zinc-aluminum-magnesium coated steel sheet resistant to filiform corrosion as described in the first aspect, the method comprising:

[0054] S1, hot-dip plating the steel substrate to obtain a zinc-aluminum-magnesium coated steel plate;

[0055] S2, cooling the zinc-aluminum-magnesium coated steel plate.

[0056] In some embodiments, the bath temperature of the hot-dip plating is 450°C to 500°C.

[0057] 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, it will be difficult to form Mg-Sb compounds in the coating. This is because the binding temperature of Mg and Sb in the plating solution is relatively high, so the plating solution temperature is required to be not less than 450°C. However, if the plating solution temperature is too high, a coarse, blocky Mg-Sb phase will be formed in the coating, or the needle-shaped Mg-Sb phase will be too long, so that the effect of the Mg-Sb phase is weakened, and the coating becomes brittle. Therefore, the plating solution temperature cannot exceed 500°C. Exemplarily, the plating solution temperature can be 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, etc.

[0058] The product prepared by the method for preparing zinc-aluminum-magnesium coated steel plate resistant to filiform corrosion is the above-mentioned zinc-aluminum-magnesium coated steel plate resistant to filiform corrosion. Since the method for preparing zinc-aluminum-magnesium coated steel plate resistant to filiform corrosion adopts part or all of the technical solutions of the embodiment of the zinc-aluminum-magnesium coated steel plate resistant to filiform corrosion, it at least has all the beneficial effects brought by the technical solutions of the zinc-aluminum-magnesium coated steel plate resistant to filiform corrosion, which will not be repeated here one by one.

[0059] The present application is further described below in conjunction with specific embodiments. The experimental methods in the following embodiments that do not specify specific conditions are usually measured in accordance with national standards / industry standards; if there are no corresponding national standards / industry standards, they are measured in accordance with common international standards, conventional conditions, or conditions recommended by the manufacturer.

[0060] A steel plate with a thickness of 1.0 mm and a width of 1500 mm was used as the substrate, and the coating weight was 100 g / m2 on both sides. The characteristics of Examples 1-13 of the present invention and Comparative Examples 1-5 are shown in Table 1.

[0061] Table 1

[0062]

[0063]

[0064] The preparation process conditions of Examples 1-13 of the present invention and Comparative Examples 1-5 are shown in Table 2.

[0065] The zinc-aluminum-magnesium coated steel sheets prepared in the above-mentioned Examples 1-13 and Comparative Examples 1-5 were subjected to a filiform corrosion resistance evaluation experiment: a layer of 20 micron thick PVB organic film was coated on the surface of the zinc-aluminum-magnesium coating, and then the surface of the organic film was scratched with a scratch width of 1 mm and a scratch depth reaching the steel substrate. 5 μL of acetic acid solution was injected into the scratch position, and the pH of the acetic acid solution was 3. The samples were then placed in a constant temperature and humidity environment (40°C, 86% RH) and stored for 4 weeks. The maximum length of filiform corrosion on the sample surface was then evaluated according to GB / T 30789.9. The longer the corrosion filaments, the more likely filiform corrosion will occur. If the length of the filiform corrosion is no more than 2 mm, the filiform corrosion resistance is excellent. If the length of the filiform corrosion exceeds 2 mm but is less than 4 mm, the filiform corrosion resistance is good (▲), and if the length of the filiform corrosion exceeds 4 mm, the filiform corrosion resistance is poor (×).

[0066] The zinc-aluminum-magnesium coated steel sheets prepared in the above examples 1-13 and comparative examples 1-5 were evaluated for coating brittleness: the samples were bent 180° by a bending method, and then the coating cracking and peeling at the bending position were observed. If the coating cracked or peeled at the bending position, the coating brittleness was poor (×), otherwise the coating brittleness was excellent.

[0067] The zinc-aluminum-magnesium coated steel plates prepared in the above-mentioned Examples 1-13 and Comparative Examples 1-5 were subjected to a neutral salt spray test, and the average thickness of the coating before corrosion and the average thickness of the coating after corrosion of the zinc-aluminum-magnesium coated steel 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.

[0068] Average corrosion rate = (average thickness of coating before corrosion - average thickness of coating after corrosion) / corrosion time (μm / h).

[0069] If the average corrosion rate of the coating does not exceed 0.03 microns / hour, the coating has excellent corrosion resistance. If the average corrosion rate of the coating exceeds 0.03 μm / hour, the corrosion resistance of the coating is poor (×).

[0070] The experimental evaluation results are shown in Table 2.

[0071] Table 2

[0072]

[0073] It can be seen from Tables 1 to 2 that in Examples 1 to 13, the chemical composition and characteristics of the zinc-aluminum-magnesium coatings are all within the required range of the present invention, and the corrosion resistance is good.

[0074] Attached Figure 2-3 Detailed description:

[0075] Figure 2 The microstructure diagram provided in Example 7 of the present application; Figure 2 As shown, the large white blocks in the microstructure are Zn, and the long strips are Sb that reacts with Mg to form Mg-Sb compounds.

[0076] Figure 3 The microstructure diagram provided for comparative example 2 of this application; Figure 3 As shown, the large white block in the microstructure is Zn, and the rest is eutectic structure.

[0077] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0078] The method for preparing the zinc-aluminum-magnesium coated steel plate provided by the embodiment of the present invention is simple and easy to operate, has low production cost, and is easy to promote and use.

[0079] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. It will be apparent to those skilled in the art that various modifications to these embodiments are possible, and 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 the embodiments shown in the present application, but will conform to the widest range consistent with the principles and novel features applied for by the present application.

Claims

1. A zinc-aluminum-magnesium coated steel sheet resistant to filiform corrosion, 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, by mass fraction, Mg: 1% to 4%, Al: 1% to 4%, Sb: 0.1% to 1%, and matrix element Zn; The zinc-aluminum-magnesium coating contains a Mg-Sb compound.

2. The coated steel sheet according to claim 1, characterized in that: The volume fraction of the Mg—Sb compound is ≥ 0.1%.

3. The coated steel sheet according to claim 1, characterized in that: The volume fraction of the eutectic structure on the surface of the zinc-aluminum-magnesium coating is ≤20%.

4. The coated steel sheet according to claim 1, characterized in that: The volume fraction of the eutectic structure on the surface of the zinc-aluminum-magnesium coating is ≥70%.

5. The coated steel sheet according to claim 1, characterized in that: The chemical composition of the zinc-aluminum-magnesium coating satisfies: [Mg] = (2-10) × [Sb], In the formula, [Mg] represents the mass fraction of Mg, and [Sb] represents the mass fraction of Sb.

6. The coated steel sheet according to claim 1, characterized in that: The chemical composition of the zinc-aluminum-magnesium coating satisfies: Al+Mg≤2.5%, wherein Al+Mg represents the sum of the mass fractions of Al and Mg.

7. The coated steel sheet according to claim 1, characterized in that: The chemical composition of the zinc-aluminum-magnesium coating satisfies: Al+Mg≥5%, wherein Al+Mg represents the sum of the mass fractions of Al and Mg.

8. The coated steel sheet according to claim 1, characterized in that: The Mg-Sb compound is needle-shaped, and the average length of the Mg-Sb compound is 100 μm to 500 μm.

9. A method for preparing a zinc-aluminum-magnesium coated steel sheet resistant to filiform corrosion according to any one of claims 1 to 8, characterized in that: The method comprises: Hot-dip coating the steel substrate to obtain a zinc-aluminum-magnesium coated steel plate; The zinc-aluminum-magnesium coated steel sheet is cooled.

10. The method according to claim 9, characterized in that The bath temperature of the hot-dip plating is 450°C to 500°C.

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