Zinc-aluminum-magnesium coating, zinc-aluminum-magnesium coated steel sheet and manufacturing method thereof

Abstract

This application relates to the field of metal material processing, and more particularly to a zinc-aluminum-magnesium coating, a zinc-aluminum-magnesium coated steel sheet, and a method for manufacturing the same. The coating comprises the following chemical components: Al, Mg, Si, Ti, B, and V, with the remainder being Zn and unavoidable impurities; the Ti content is 0.025% to 0.125% by weight, and the B content is 0.009% to 0.014% by weight. This application addresses the technical issues of zinc-aluminum-magnesium coated steel sheets prone to surface blackening and difficulty controlling surface quality.

Description

Technical Field

[0001] The present application relates to the field of metal material processing, and in particular to a zinc-aluminum-magnesium coating, a zinc-aluminum-magnesium coated steel plate and a manufacturing method thereof. Background Art

[0002] Hot-dip galvanized aluminum-magnesium coated steel sheets offer excellent corrosion resistance and are widely used in the construction, home appliance, and photovoltaic industries. High-aluminum zinc-aluminum-magnesium products, with an Al content exceeding 50% and a certain amount of Mg added, offer superior surface and cut corrosion resistance compared to standard coated products, demonstrating significant social benefits and application value.

[0003] However, because the active metal Mg easily reacts with water to form hydroxide, the surface of the high-aluminum-zinc-aluminum-magnesium coating is prone to blackening during transportation and use, affecting the product's appearance and promotion. Moreover, the addition of Mg to the coating makes the surface susceptible to oxidation during the hot-dip plating process, making the coating surface quality difficult to control.

[0004] Chinese patent CN112410706A discloses a highly corrosion-resistant aluminum-zinc-magnesium alloy coating with uniform crystals and its formation process. Nano-aluminum oxide particles are added to the plating bath to form a highly corrosion-resistant aluminum-zinc-magnesium alloy coating with uniform crystals. However, due to the high melting point and low density of Al2O3, solid Al2O3 particles remain suspended in the plating bath, becoming impurities that can affect the surface quality of the aluminum-zinc-magnesium plate.

[0005] In summary, in the prior art, hot-dip galvanized aluminum-magnesium coated steel sheets have the problems of easy surface blackening and difficult surface quality control. Summary of the Invention

[0006] The present application provides a zinc-aluminum-magnesium coating, a zinc-aluminum-magnesium coated steel plate and a manufacturing method thereof, in order to solve the problem in the prior art that the surface of the hot-dip zinc-aluminum-magnesium coated steel plate is easily blackened and the surface quality is difficult to control.

[0007] In a first aspect, the present application provides a zinc-aluminum-magnesium coating, wherein the coating comprises the following chemical components:

[0008] Al, Mg, Si, Ti, B, V, the rest are Zn and inevitable impurities; among them,

[0009] The Ti content is 0.025 wt% to 0.125 wt%;

[0010] The content of B is 0.005 wt% to 0.014 wt%.

[0011] Optionally, in the chemical composition, the weight ratio of Ti to B is 4.0 to 10.0.

[0012] Optionally, in the chemical composition, the Al content is 54.0 wt% to 56.0 wt%, the Mg content is 1.0 wt% to 2.2 wt%, the Si content is 1.4 wt% to 1.7 wt%, and the V content is ≤0.0015 wt%.

[0013] Optionally, the coating includes at least one of the following chemical substances: TiAl3, and / or TiB2.

[0014] Optionally, the average diameter of the TiAl3 is less than 20 μm, and the average diameter of the TiB2 is less than 2 μm.

[0015] Optionally, the surface crystal diameter of the coating is ≤2.0 mm.

[0016] In a second aspect, the present application provides a zinc-aluminum-magnesium coated steel plate, the steel plate comprising: a steel plate substrate, and

[0017] The zinc-aluminum-magnesium coating of the first aspect;

[0018] The zinc-aluminum-magnesium coating is attached to at least a portion of the surface of the steel plate substrate.

[0019] In a third aspect, the present application provides a method for manufacturing a zinc-aluminum-magnesium coated steel sheet, which is used to manufacture the zinc-aluminum-magnesium coated steel sheet described in the second aspect, and the method comprises:

[0020] The chilled plate is degreased and then continuously annealed to obtain a steel plate matrix;

[0021] The steel plate substrate is placed in a plating solution for hot dip plating, so that the plating solution adheres to at least a portion of the surface of the steel plate substrate to obtain a zinc-aluminum-magnesium coated steel plate.

[0022] Optionally, the raw materials of the plating solution include: aluminum-based master alloy containing titanium and boron.

[0023] Optionally, the aluminum-based master alloy containing titanium and boron comprises the following chemical components:

[0024] Ti, B, V, the rest are Al and inevitable impurities; among them,

[0025] The content of Ti is 4.4 wt% to 6.0 wt%; the content of B is 0.5 wt% to 1.2 wt%; the content of V is ≤ 0.03 wt%;

[0026] The weight ratio of Ti to B is 4.0 to 10.0;

[0027] The aluminum-based master alloy containing titanium and boron comprises at least one of the following chemical substances: TiAl3, TiB2;

[0028] The average diameter of the TiAl3 is less than 20 μm, and the average diameter of the TiB2 is less than 2 μm.

[0029] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0030] In the embodiment of the present application, Ti and B are added to the chemical composition of the coating, TiAl3 and TiB2 are effective heterogeneous nucleation cores, and promote Al phase crystallization; the coating contains fine TiAl3 or TiB2 particles; the coating chemical composition is designed with a reasonable Ti / B weight ratio; in the manufacturing method of the zinc-aluminum-magnesium coated steel plate, a titanium-boron-containing aluminum-based intermediate alloy with a certain Ti content and Ti / B weight ratio and containing fine TiAl3 or TiB2 particles is added to the plating solution to control the Ti content and Ti / B weight ratio of the plating solution; the above design promotes the refinement of the coating, effectively improves the blackening resistance of the coating surface, and is conducive to obtaining excellent coating surface quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0032] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0033] Figure 1 A schematic flow chart of a method for manufacturing a zinc-aluminum-magnesium coated steel plate provided in an embodiment of the present application;

[0034] Figure 2 This is a scanning electron microscope image of the aluminum-based master alloy containing titanium and boron provided in Example 1 of the present application, where 1 is TiAl3 and 2 is TiB2. DETAILED DESCRIPTION

[0035] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0036] 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 hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have 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 herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0037] In this application, unless otherwise indicated, directional words such as "upper" and "lower" refer specifically to the directions of the drawings in the accompanying drawings. In addition, in the description of this application specification, the terms "including" and "comprising" mean "including but not limited to".

[0038] In this document, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. In this document, "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this document, "at least one" refers to one or more, and "plurality" refers to 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 represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0039] 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.

[0040] In a first aspect, the present application provides a zinc-aluminum-magnesium coating, wherein the coating comprises the following chemical components:

[0041] Al, Mg, Si, Ti, B, V, the rest are Zn and inevitable impurities; among them,

[0042] The Ti content is 0.025 wt% to 0.125 wt%;

[0043] The content of B is 0.005 wt% to 0.014 wt%.

[0044] The composition of the zinc-aluminum-magnesium coating is shown in Table 1. The hot-dip zinc-aluminum-magnesium coated steel plate in the embodiment of the present application has good blackening resistance and few surface defects, and can be used in the construction, home appliances, photovoltaic and other industries.

[0045] The effect of controlling the Ti content to 0.025 wt% to 0.125 wt% is as follows: Ti forms TiB2 phase with B, and Ti forms TiAl3 phase with Al. The TiB2 and TiAl3 phases act as heterogeneous nucleation sites to promote Al crystallization. They can also undergo peritectic reactions to refine the Al phase crystallization, thereby improving the relative distribution uniformity of the Mg-rich phase, Al-rich phase, and Zn-rich phase in the coating, inhibiting electrochemical corrosion in the presence of water, and effectively improving the blackening resistance of the coating surface. Too low a Ti content will not effectively refine the coating, while too high a Ti content will easily promote the formation of Al-Fe-Si zinc slag in the plating solution, ultimately affecting the surface quality of the hot-dip galvanized aluminum-magnesium coated steel sheet. Specifically, in the embodiments of the present application, the Ti content can be 0.025 weight%, 0.03 weight%, 0.035 weight%, 0.04 weight%, 0.045 weight%, 0.05 weight%, 0.055 weight%, 0.06 weight%, etc.; preferably, the Ti content is 0.125 weight%, 0.025 weight%, 0.05 weight%, 0.04 weight%.

[0046] The effect of controlling the boron content to 0.005% to 0.014% by weight: B exists in the titanium-boron-containing aluminum-based master alloy as TiB2. TiB2 is insoluble in the plating solution. During the cooling process of the coating, TiB2 acts as a heterogeneous nucleation site, refining the surface Al phase crystallization and promoting the precipitation of TiAl3 on the TiB2 surface, further promoting Al phase crystallization and refinement. This improves the relative uniformity of the Mg-rich phase, Al-rich phase, and Zn-rich phase in the coating, inhibiting electrochemical corrosion in the presence of water, and effectively improving the coating's surface resistance to blackening. Too low a boron content can lead to the formation of zinc slag in the plating solution, while too high a boron content can compromise the coating's fine coating effect. Specifically, in the embodiments of the present application, the content of B can be 0.005 weight%, 0.006 weight%, 0.007 weight%, 0.008 weight%, 0.009 weight%, 0.010 weight%, 0.012 weight%, 0.013 weight%, 0.014 weight%, etc.; preferably, the content of B is 0.0135 weight%, 0.0052 weight%, 0.0095 weight%, 0.009 weight%.

[0047] The role of Zn: Zn is dissolved in the Al-rich phase in the coating and distributed between Al-rich dendrites, playing a role in protecting the cathode, and the corrosion products can reduce the surface corrosion rate. Too low Zn content will reduce the corrosion resistance of the coating.

[0048] In some embodiments, in the chemical composition, the weight ratio of Ti to B is 4.0 to 10.0.

[0049] The effect of controlling the weight ratio of Ti to B to be 4.0 to 10.0: Under the condition of an appropriate Ti / B weight ratio, B exists entirely in the form of TiB2 in the aluminum-based master alloy containing titanium and boron, acting as a heterogeneous nucleation site to promote Al crystallization. A Ti / B ratio that is too high tends to promote the formation of zinc slag in the plating solution, affecting the surface quality of the hot-dip galvanized aluminum-magnesium coated steel sheet. A Ti / B ratio that is too low tends to form AlB2 phase, affecting the coating refinement effect. Furthermore, the average diameter of the TiB2 phase is below 5 μm, which does not affect the surface quality of the coating. Specifically, in the embodiments of the present application, Ti / B can be 4, 5, 6, 7, 8, 9, 10, etc.; preferably, Ti / B is 9.26, 4.79, 5.26, or 4.44.

[0050] In some embodiments, in the coating, the content of Al is 54.0 wt% to 56.0 wt%, the content of Mg is 1.0 wt% to 2.2 wt%, the content of Si is 1.4 wt% to 1.7 wt%, and the content of V is ≤0.0015 wt%.

[0051] The effect of controlling the Al content to be 54.0 wt% to 56.0 wt% is that Al is a dendritic crystal in the coating, which easily forms oxides to hinder the corrosion of the coating and improve the corrosion resistance of the coating. Under acidic or neutral conditions, too high or too low an Al content will increase the corrosion current and reduce the corrosion resistance of the coating. Specifically, in the embodiment of the present application, the Al content can be 54.0 wt%, 54.5 wt%, 55.0 wt%, 55.5 wt%, 56.0 wt%, etc. Preferably, the Al content is

[0052] 55.0 wt%, 54.0 wt%, 54.8 wt%, 55.8 wt%.

[0053] The effect of controlling the Mg content to 1.0 wt% to 2.2 wt% is as follows: it forms a MgZn2 phase with Zn to suppress the increase in pH value and stabilize the surface protective corrosion products, thereby improving the corrosion resistance of the coating. If the Mg content is too low, it will affect the corrosion resistance of the coating; if the Mg content is too high, it will form galvanic corrosion with the Al-rich phase and the Al-rich phase-Zn-rich phase in the presence of water on the surface to produce hydroxides, causing the surface to turn black. Specifically, in the embodiments of the present application, the Mg content can be 1.0 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2.0 wt%, 2.2 wt%, etc.; preferably, the Mg content is 2.2 wt%, 1.2 wt%, 1.8 wt%, 1.0 wt%.

[0054] The purpose of controlling the Si content to 1.4 wt% to 1.7 wt% is to inhibit Al diffusion during the hot-dip plating process and to inhibit Al from reacting with Fe in the substrate to form an alloy layer, thereby ensuring the uniformity of the coating. Too high or too low a Si content will affect the thickness of the alloy layer, resulting in uneven coating. Specifically, in the embodiments of the present application, the Si content can be 1.4 wt%, 1.45 wt%, 1.50 wt%, 1.55 wt%, 1.60 wt%, 165 wt%, 1.70 wt%, etc.; preferably, the Si content is 1.53 wt%, 1.65 wt%, 1.58 wt%, or 1.57 wt%.

[0055] The purpose of controlling the V content to ≤ 0.0015 wt% is that V and Ti are symbiotic alloying components. Adding Ti to aluminum-based master alloys often results in a small amount of V residue. Excessive V content can easily form Al-V-Ti zinc slag, affecting the surface quality of the coating. Specifically, in the embodiments of the present application, the V content can be 0.0015 wt%, 0.001 wt%, 0.0005 wt%, etc.; preferably, the V content is 0.0006 wt%, 0.0005 wt%, 0.0008 wt%, or 0.0015 wt%.

[0056] In some embodiments, the coating comprises at least one of the following chemical species: TiAl3, TiB2.

[0057] In some embodiments, the size of the TiAl3 is less than 20 μm, and the size of the TiB2 is less than 2 μm.

[0058] Controlling the size of TiAl3 to less than 20 μm and the size of TiB2 to less than 2 μm not only achieves a better coating refinement effect but also contributes to obtaining a better coating surface quality. Specifically, as shown in Table 2, in the embodiments of the present application, the TiAl3 particle size can be 19 μm, 17 μm, 15 μm, 13 μm, 11 μm, etc., and the average diameter of TiB2 can be 1.8 μm, 1.6 μm, 1.4 μm, 1.0 μm, etc.; preferably, the average diameter of TiAl3 is 18.4 μm, 13.3 μm, 11.5 μm, 10 μm, and the average diameter of TiB2 is 1.8 μm, 0.9 μm, 0.6 μm, 0.5 μm.

[0059] In some embodiments, the surface crystal diameter of the coating is ≤2.0 mm.

[0060] The crystal flowers on the surface of the coating are a hexagonal structure formed by a dendritic Al-rich phase and a Zn-rich phase and a Mg-rich phase between the dendrites. The crystal flower size is controlled within a small range, and the relative distribution of the Al-rich phase, the Zn-rich phase and the Mg-rich phase is more uniform, which inhibits electrochemical corrosion in the presence of water and effectively improves the blackening resistance of the coating surface. The larger the crystal flower size, the lower the inhibitory effect, and the worse the blackening resistance of the coating surface. Specifically, in the embodiment of the present application, the surface crystal flower diameter of the coating can be 2.0 mm, 1.8 mm, 1.6 mm, 1.4 mm, 1.2 mm, etc.; preferably, the surface crystal flower diameter of the coating is 0.9 mm, 2.0 mm, 1.5 mm, 1.2 mm.

[0061] In a second aspect, the present application provides a zinc-aluminum-magnesium coated steel plate, the steel plate comprising: a steel plate substrate, and the zinc-aluminum-magnesium coating described in the first aspect;

[0062] The zinc-aluminum-magnesium coating is attached to at least a portion of the surface of the steel plate substrate.

[0063] The zinc-aluminum-magnesium coated steel plate is realized based on the above-mentioned zinc-aluminum-magnesium coating. The specific steps of the zinc-aluminum-magnesium coating can refer to the above-mentioned embodiments. Since the zinc-aluminum-magnesium coating adopts part or all of the technical solutions of the above-mentioned embodiments, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be repeated here.

[0064] In the third aspect, the present application provides a method for manufacturing a zinc-aluminum-magnesium coated steel sheet, which is used to manufacture the zinc-aluminum-magnesium coated steel sheet described in the second aspect. Figure 1 , the method comprising:

[0065] S1. Degreasing the chilled plate and then continuously annealing it to obtain a steel plate matrix;

[0066] S2. Place the steel plate substrate in a plating solution for hot dip plating, so that the plating solution adheres to at least a portion of the surface of the steel plate substrate to obtain a zinc-aluminum-magnesium coated steel plate.

[0067] In the embodiment of this application, the hot-dip coating step is completed in the main zinc pot. The main zinc pot is replenished with zinc liquid via a pre-melting pot, and the pre-melting pot plating liquid flows into the main zinc pot via a high-temperature chute. The high-temperature chute prevents the zinc liquid from solidifying due to rapid heat dissipation. Solidified zinc liquid can cause chute blockage and increase temperature and composition deviations of the zinc liquid in the main zinc pot, ultimately affecting the surface quality of the hot-dip galvanized aluminum-magnesium coated steel sheet.

[0068] In some embodiments, the raw materials of the plating solution include: aluminum-based master alloy containing titanium and boron, see Figure 2 .

[0069] In some embodiments, the aluminum-based master alloy containing titanium and boron comprises the following chemical composition:

[0070] Ti, B, V, the rest are Al and inevitable impurities; among them,

[0071] The content of Ti is 4.4 wt% to 6.0 wt%; the content of B is 0.5 wt% to 1.2 wt%; the content of V is ≤ 0.03 wt%;

[0072] The weight ratio of Ti to B is 4.0 to 10.0;

[0073] The aluminum-based master alloy containing titanium and boron comprises at least one of the following chemical substances: TiAl3, TiB2;

[0074] The average diameter of the TiAl3 is less than 20 μm, and the average diameter of the TiB2 is less than 2 μm.

[0075] The composition of the aluminum-based master alloy containing titanium and boron can be seen in Table 3, and the microscopic morphology of the aluminum-based master alloy containing titanium and boron can be seen in Figure 2 In the embodiments of the present application, the Ti content in the Ti- and B-containing aluminum-based master alloy may be 4.4 weight %, 4.6 weight %, 4.8 weight %, 5.0 weight %, 5.2 weight %, 5.4 weight %, 5.6 weight %, 5.8 weight %, 6.0 weight %, etc.; preferably, the Ti content is 5.5 weight %, 4.59 weight %, 5.01 weight %, or 4.93 weight %.

[0076] The content of B can be 0.5 weight%, 0.6 weight%, 0.7 weight%, 0.8 weight%, 0.9 weight%, 1.0 weight%, 1.1 weight%, 1.2 weight%, etc.; preferably, the content of B is 0.59 weight%, 0.95 weight%, 0.93 weight%, 1.07 weight%.

[0077] The V content may be 0.03 wt%, 0.01 wt%, 0.005 wt%, etc. Preferably, the V content is 0.003 wt%, 0.004 wt%, 0.009 wt%, or 0.03 wt%.

[0078] The positive effect of controlling the weight ratio of Ti and B to 4.0-10.0: Under the appropriate Ti / B weight ratio, all B in the Ti- and B-containing aluminum-based master alloy exists in the form of TiB2, and the remaining Ti exists in the form of TiAl3. After adding the high-temperature melt, TiAl3 dissolves, while TiB2 remains insoluble. During the cooling process after the steel plate is plated, the Ti in the plating solution reprecipitates as the TiAl3 phase. TiAl3 and TiB2 are effective heterogeneous nucleation cores, promoting the crystallization of the Al phase, refining the coating, and effectively improving the blackening resistance of the coating surface. Too high a Ti / B ratio can easily promote the formation of zinc slag in the plating solution, affecting the surface quality of the coating. Too low a Ti / B ratio can easily form the AlB2 phase, affecting the coating refinement effect. Specifically, Ti / B can be 4, 5, 6, 7, 8, 9, 10, etc.; preferably, Ti / B is 9.32, 4.83, 5.39, or 4.61.

[0079] In this titanium-boron-containing aluminum-based master alloy, controlling the average diameter of TiAl3 to less than 20 μm and the average diameter of TiB2 to less than 2 μm has the positive effect of controlling the particle size of TiAl3 and TiB2, not only effectively refining the coating, but also improving the surface quality of the coating. Specifically, as shown in Table 4, in the embodiments of the present application, the particle size of TiAl3 can be 19 μm, 17 μm, 15 μm, 13 μm, 11 μm, etc., and the average diameter of TiB2 can be 1.8 μm, 1.6 μm, 1.4 μm, 1.0 μm, etc.; preferably, the average diameter of TiAl3 is 19.6 μm, 15.7 μm, 15.0 μm, and 12.5 μm, and the average diameter of TiB2 is 1.8 μm, 1.0 μm, 0.7 μm, and 0.6 μm. Coarse TiAl3 and TiB2 particle sizes reduce the coating refinement effect and easily cause zinc slag problems, affecting the surface quality of the coating. Controlling the particle size of TiAl3 and TiB2 to be small can better achieve the effect of coating refinement and help obtain better coating surface quality.

[0080] The zinc-aluminum-magnesium coated steel plate is realized based on the manufacturing method of the above-mentioned zinc-aluminum-magnesium coated steel plate. The specific steps of the manufacturing method of the zinc-aluminum-magnesium coated steel plate can refer to the above-mentioned embodiment. Since the zinc-aluminum-magnesium coated steel plate adopts part or all of the technical solutions of the above-mentioned embodiment, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiment, which will not be repeated here one by one.

[0081] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods in the following examples where specific conditions are not specified are usually measured in accordance with national standards. If there are no corresponding national standards, then the methods are carried out in accordance with general international standards, conventional conditions, or according to the conditions recommended by the manufacturer.

[0082] Table 1 Weight percentage of each chemical component of zinc-aluminum-magnesium coatings in Examples 1-5 and Comparative Examples 1-2 (the balance is Zn and unavoidable impurities), Ti / B weight ratio, coating thickness is 120 g / m 2 .

[0083]

[0084]

[0085] Table 2 Average diameters of TiAl3 and TiB2 in the coatings of the steel sheets of the examples and comparative examples.

[0086] Serial number <![CDATA[Average diameter of TiAl3 (μm)]]> <![CDATA[Average diameter of TiB2 (μm)]]> Comparative Example 1 none none Comparative Example 2 30 none Example 1 18.4 1.8 Example 2 13.3 0.9 Example 3 10.0 0.6 Example 4 11.5 0.5

[0087] Table 3 shows the weight percentages of the components in the aluminum-based master alloys containing titanium and boron used in Examples 1-5, with the remainder being Al and unavoidable impurities.

[0088]

[0089]

[0090] Table 4 Average diameters of TiAl3 and TiB2 particles in the aluminum-based master alloys containing titanium and boron according to Examples 1-5.

[0091] Serial number <![CDATA[Average diameter of TiAl3 (μm)]]> <![CDATA[Average diameter of TiB2 (μm) <!-- 7 -->]]> Example 1 19.6 1.8 Example 2 15.7 1.0 Example 3 15.0 0.7 Example 4 12.5 0.6

[0092] The surfaces of the zinc-aluminum-magnesium coated steel sheets of the above-mentioned embodiments and comparative examples were observed using a scanning electron microscope. The average diameters of 10 crystal flowers of each zinc-aluminum-magnesium coated steel sheet were taken. The results are shown in Table 5.

[0093] Table 5: Crystal diameters on the steel plate surfaces of Examples 1-5 and Comparative Examples 1-2.

[0094] Serial number Crystal flower diameter (mm) Comparative Example 1 4.2 Comparative Example 2 2.8 Example 1 0.9 Example 2 2 Example 3 1.5 Example 4 1.2

[0095] Table 6 Surface color difference ΔE of zinc-aluminum-magnesium coated steel plates before and after the experiment of Examples 1-5 and Comparative Examples 1-2.

[0096] Serial number ΔE Comparative Example 1 6.63 Comparative Example 2 4.32 Example 1 0.4 Example 2 1.2 Example 3 0.6 Example 4 1.0

[0097] The surface defects of the zinc-aluminum-magnesium coated steel sheets of Examples 1-5 and Comparative Examples 1-2 were visually observed and measured with a ruler. The number of defects within an area of 100*100 mm was counted. The average value of 10 different areas for each zinc-aluminum-magnesium coated steel sheet was taken. The surface defect status is shown in Table 7. Table 7 Surface Defects of the Zinc-Aluminum-Magnesium Coated Steel Sheets of Examples 1-5 and Comparative Examples 1-2: Statistics of the number of defects within an area of 100*100 mm.

[0098] Serial number >500μm defect count Number of defects ≤500μm Comparative Example 1 0 15 Comparative Example 2 2 21 Example 1 0 8 Example 2 0 5 Example 3 0 4 Example 4 0 10

[0099] As can be seen from Table 5, the hot-dip galvanized aluminum-magnesium coated steel plates of Examples 1-4 of this case have uniform coating distribution on the surface and small crystal diameter, which can significantly inhibit electrochemical corrosion in the presence of water and effectively improve the blackening resistance of the coating surface.

[0100] As can be seen from Table 6, the surface color difference ΔE of the hot-dip galvanized aluminum-magnesium coated steel plates of Examples 1-4 tested after 120 hours of testing at 50°C and 95% relative humidity in an ESPEC-SETH-Z-02R damp heat test chamber is significantly smaller than that of the comparative example, indicating that the steel plates of the examples have good blackening resistance.

[0101] It can be seen from Table 7 that the number of defects within >500μm of the hot-dip galvanized aluminum-magnesium coated steel sheets of Examples 1-4 is 0, and the number of defects within ≤500μm is significantly smaller than that of the comparative example, indicating that the zinc-aluminum-magnesium coated steel sheets of the present application have good surface quality.

[0102] In Comparative Examples 1-2, the coating basically does not contain Ti and B, or the Ti / B weight ratio is too high or too low, and does not contain TiAl3 and TiB2 particles or the particle size is too large, resulting in a larger crystal flower diameter of the coated steel plate, a larger color difference ΔE of the steel plate before and after the experiment, and a large number of surface defects, resulting in poor surface weight and blackening resistance of the coated steel plate.

[0103] In Examples 1-4, a titanium-boron-containing aluminum-based master alloy is added to the pre-melting pot, and the Ti / B weight ratio in the titanium-boron-containing aluminum-based master alloy is regulated, thereby regulating the particle size of TiAl3 and TiB2 in the titanium-boron-containing aluminum-based master alloy, thereby obtaining a coated steel plate with better surface quality and blackening resistance.

[0104] In summary, the hot-dip galvanized aluminum-magnesium coated steel plate described in this application has good blackening resistance and surface quality.

[0105] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present 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 the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A zinc-aluminum-magnesium coating, characterized in that: The coating consists of the following chemical components: The Al content is 54.0% to 56.0% by weight, the Mg content is 1.0% to 2.2% by weight, the Si content is 1.4% to 1.7% by weight, the Ti content is 0.025% to 0.125% by weight, the B content is 0.005% to 0.014% by weight, the V content is ≤0.0015% by weight, and the rest is Zn and unavoidable impurities; the coating includes at least one of the following chemical substances: TiAl3 and TiB2, the average diameter of the TiAl3 is <20μm, the average diameter of the TiB2 is <2μm, the surface crystal flowers of the coating are dendritic Al-rich phases and a hexagonal structure formed by the Zn-rich phase and the Mg-rich phase between the dendrites, and the surface crystal flower diameter of the coating is ≤2.0mm.

2. The coating according to claim 1, wherein In the chemical composition, the weight ratio of Ti to B is 4.0 to 10.

0.

3. A zinc-aluminum-magnesium coated steel plate, characterized in that: The steel plate comprises: a steel plate substrate, and The zinc-aluminum-magnesium coating according to any one of claims 1-2; The zinc-aluminum-magnesium coating is attached to at least a portion of the surface of the steel plate substrate.

4. A method for manufacturing a zinc-aluminum-magnesium coated steel plate, characterized in that: For manufacturing the zinc-aluminum-magnesium coated steel sheet according to claim 3, the method comprises: The chilled plate is degreased and then continuously annealed to obtain a steel plate matrix; The steel plate substrate is placed in a plating solution for hot dip plating, so that the plating solution adheres to at least a portion of the surface of the steel plate substrate to obtain a zinc-aluminum-magnesium coated steel plate.

5. The method according to claim 4, characterized in that The raw materials of the plating solution include: aluminum-based master alloy containing titanium and boron.

6. The method according to claim 5, characterized in that The aluminum-based master alloy containing titanium and boron comprises the following chemical components: Ti, B, V, the rest are Al and inevitable impurities; among them, The content of Ti is 4.4 wt% to 6.0 wt%; the content of B is 0.5 wt% to 1.2 wt%; the content of V is ≤ 0.03 wt%; The weight ratio of Ti to B is 4.0 to 10.0; The aluminum-based master alloy containing titanium and boron comprises at least one of the following chemical substances: TiAl3, TiB2; The average diameter of the TiAl3 is less than 20 μm, and the average diameter of the TiB2 is less than 2 μm.

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