Alloy, preparation method and application thereof

Abstract

The present application provides an alloy comprising the following elements in weight percentage: 1-4% Al, 1-4% Mg, 0.0005-0.0020% rare earth elements, and 92-98% Zn; the rare earth element is at least one of La and Ce; the alloy surface comprises an initial solidification phase and a first eutectic structure, wherein the first eutectic structure is a eutectic structure of Zn, Al, and Mg-Zn compounds, and at least 80% of the first eutectic structure exists in the form of grains no larger than 100 μm in size. The alloy provided in the embodiments of the present application can avoid surface blackening and avoid excessive stress concentration at the interface between the eutectic structure and the initial solidification phase, resulting in an uneven morphology of the coating surface.

Description

Technical Field

[0001] The present application relates to the field of metal anti-corrosion, and in particular to an alloy that can be used for anti-corrosion coating. Background Art

[0002] Zinc-aluminum-magnesium (Zn-Aluminum-Mg)-coated steel sheets are often used in applications such as automobiles, home appliances, and steel structures, where corrosion resistance is a high priority. The Zn-Mg-Aluminum coating on Zn-Aluminum-Mg-coated steel sheets is an alloy primarily composed of zinc, magnesium, and aluminum. Existing Zn-Mg-Aluminum coatings are prone to deformation during processing, resulting in an uneven surface finish that impacts the user experience. Summary of the Invention

[0003] The embodiments of the present application provide an alloy, a preparation method, and an application thereof to solve the technical problem that the surface of the zinc-magnesium-aluminum coating becomes uneven after processing and deformation.

[0004] In a first aspect, an embodiment of the present application provides an alloy comprising the following elements in weight percentage: 1-4% Al, 1-4% Mg, 0.0005-0.0020% rare earth elements, and 92-98% Zn; the rare earth element is at least one of La and Ce; the surface of the alloy comprises an initial solidified phase and a eutectic structure, at least 80% of the area of the surface of the initial solidified phase is occupied by a micro-solidified phase having a surface size of no more than 100 μm, and the eutectic structure is a eutectic structure of Zn, Al, and a Mg-Zn compound.

[0005] In some embodiments of the present application, the alloy includes zinc compound particles containing rare earth.

[0006] In some embodiments of the present application, the diameter of the particles is no greater than 5 μm.

[0007] In some embodiments of the present application, the Mg-Zn compound includes MgZn2 and Mg2Zn 11 At least one of .

[0008] In some embodiments of the present application, at least 80% of the surface area of the eutectic structure is occupied by grains with a surface size of no more than 100 μm.

[0009] In some embodiments of the present application, the alloy is composed of the following elements in weight percentage: 1-4% Al, 1-4% Mg, 0.0005-0.0020% rare earth elements, and 92-98% Zn.

[0010] In a second aspect, an embodiment of the present application provides a method for preparing an alloy, comprising the following steps:

[0011] Providing a substrate and a plating solution, wherein the elemental composition of the plating solution is completely the same as the elemental composition of the aforementioned alloy;

[0012] The alloy is formed by hot-dip plating on the substrate using the plating solution.

[0013] In a third aspect, an embodiment of the present application provides an alloy coating, wherein the material of the alloy coating is the aforementioned alloy.

[0014] In a fourth aspect, an embodiment of the present application provides a coated steel plate, wherein the coated steel plate includes a steel plate substrate and a coating provided on the steel plate substrate, wherein the coating is the aforementioned alloy coating.

[0015] In some embodiments of the present application, the surface roughness Ra of the steel plate substrate is in the range of 0.8 to 1.8 microns, and the peak number RPc is not less than 80.

[0016] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0017] The alloys provided in the embodiments of this application, by regulating the element ratios, form fine grains of Al and Zn in the eutectic structure. This increases the electrochemical reaction rate of Al and Zn, aligning the reaction rates of Al, Mg, and Zn. This allows for the rapid formation of compounds such as white basic carbonates containing Al, Mg, and Zn, rather than just black magnesium hydroxide compounds, thus preventing surface blackening. Furthermore, the addition of rare earth elements forms fine, dispersed compound particles in the coating, refining the initial solidification phase and preventing excessive stress concentration at the interface between the eutectic structure and the initial solidification phase, which can lead to an uneven coating surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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.

[0019] 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.

[0020] Figure 1 A schematic flow chart of a method for preparing an alloy provided in an embodiment of the present application;

[0021] Figure 2 This is a SEM image of the surface morphology of the alloy coating in Example 1;

[0022] Figure 3 This is the surface morphology SEM image of the alloy coating in Comparative Example 3. DETAILED DESCRIPTION

[0023] The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly presented. It should be understood by those skilled in the art that these specific embodiments and examples are intended to illustrate the present invention, rather than to limit the present invention.

[0024] Throughout this specification, unless otherwise specified, the terms used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. In the event of any conflict, the present specification shall take precedence.

[0025] 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.

[0026] In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application and are not used to limit the present application. In this application, unless otherwise specified, the directional words used, such as "upper" and "lower", specifically refer to the directions of the drawings in the accompanying drawings. In addition, in the description of the present specification, the term "including" means "including but not limited to". Various embodiments of the present invention 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 invention; 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, the range description 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 apply regardless of the range. In addition, whenever a numerical range is indicated in this document, it is meant to include any quoted number (fractional or integer) within the indicated range.

[0027] In this application, "and / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0028] In this application, "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 items 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.

[0029] In this application, relational terms such as "first" and "second" are used only 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. Moreover, the terms "comprises", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article or apparatus. In the absence of further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising the elements.

[0030] There are two problems with existing zinc-magnesium-aluminum coatings: first, when the air contains a lot of water, the magnesium element is prone to chemical reactions, causing the coating surface to turn black; second, the surface coating is prone to an uneven appearance, affecting user experience.

[0031] The technical solutions provided in the embodiments of this application are intended to solve the above technical problems, and the overall idea is as follows:

[0032] In a first aspect, the alloy includes the following elements in weight percentage: 1-4% Al, 1-4% Mg, 0.0005-0.0020% rare earth elements, and 92-98% Zn; the rare earth element is at least one of La and Ce; the surface of the alloy includes an initial solidification phase and a eutectic structure, at least 80% of the area of the surface of the initial solidification phase is occupied by a micro-solidification phase with a surface size of no more than 100 μm, and the eutectic structure is a eutectic structure of Zn, Al and Mg-Zn compound.

[0033] Regarding the surface roughness of zinc-magnesium-aluminum coatings, those skilled in the art will understand that zinc-magnesium-aluminum coatings typically contain a relatively large zinc-rich phase as a coarse initial solidification phase, with fine eutectic structures distributed between the initial solidification structures. When the coating undergoes processing deformation, the eutectic structure deforms first, and then internal stress accumulates at the interface between the eutectic structure and the initial solidification phase.

[0034] As the deformation progresses, deformation occurs inside the initial solidified phase, which is mainly composed of the zinc-rich phase.

[0035] Due to the large difference in the deformability of the initial solidified phase and the eutectic structure, a large stress accumulation occurs in the initial solidified phase, resulting in microcracks.

[0036] When these micro cracks accumulate to a certain extent, they cause the coating surface to have a macroscopic rough morphology.

[0037] The main principles involved in this application are as follows: zinc-aluminum-magnesium coatings are usually produced using a hot-dip coating process. In order to ensure that the zinc-aluminum-magnesium coating has excellent corrosion resistance, more than 1% Al is usually added to the coating. As the concentration of Al increases, a thicker inhibition layer is easily formed. This thicker inhibition layer further reduces the nucleation cores of the initial solidification phase in the coating and increases the grain size of the initial solidification phase. This makes it more likely that a macroscopically rough morphology will appear during the deformation process of the hot-dip zinc-aluminum-magnesium coating. Therefore, the Al content in the present invention is controlled to not exceed 4%.

[0038] The Mg element in the Zn-Al-Mg coating can significantly improve the corrosion resistance of the coating. In addition, the addition of Mg can form Mg-Zn compounds, which can play a role in nucleation.

[0039] The addition of trace amounts of rare earth elements can form fine, dispersed compound particles in the coating. These particles have a higher melting point than the zinc-aluminum-magnesium plating solution, allowing them to precipitate before the initial solidification phase forms. The precipitated fine, dispersed compounds serve as nucleation cores for the initial solidification phase, thereby refining it. This allows the initial solidification phase to maintain a certain degree of deformation during processing and deformation of the coating, preventing excessive stress concentration at the interface between the eutectic structure and the initial solidification phase, which can lead to an uneven surface morphology. To achieve this goal, the total amount of added rare earth elements should be above 0.0005%. However, if the addition is too high, coarse particles will form, failing to refine the grains and potentially leading to inclusion defects, which can cause surface defects during stamping. Therefore, the total amount of Ce and La elements should not exceed 0.0020%.

[0040] In some embodiments of the present application, the alloy includes zinc compound particles containing rare earth elements. The compound particles formed by rare earth elements are mainly compounds formed by rare earth elements Ce, La and zinc.

[0041] In some embodiments of the present application, the diameter of the particles is no greater than 5 μm.

[0042] Those skilled in the art will appreciate that a particle diameter of no greater than 5 μm can sufficiently refine the initial solidification phase.

[0043] In some embodiments of the present application, the Mg-Zn compound includes MgZn2 and Mg2Zn 11 At least one of .

[0044] Those skilled in the art will appreciate that the first eutectic structure includes a ternary eutectic structure. The initial solidification structure of the zinc-aluminum-magnesium coating may be an aluminum-rich phase or a zinc-rich phase, depending on the coating composition, while the ternary eutectic structure is composed of a Zn / Al / Mg-Zn compound, where the Mg-Zn compound is MgZn2 and / or Mg2Zn11.

[0045] Those skilled in the art will appreciate that the zinc-aluminum-magnesium coating may also contain a small amount of binary eutectic structures of Zn / Al, Zn / Mg-Zn compounds, and Al / Mg-Zn compounds.

[0046] In some embodiments of the present application, at least 80% of the surface area of the eutectic structure is occupied by grains with a surface size of no more than 100 μm.

[0047] Those skilled in the art will appreciate that existing zinc-magnesium-aluminum coatings are prone to blackening. When zinc-aluminum-magnesium coatings are exposed to high humidity or water, liquid water forms on the coating surface. The alloying elements in the coating can undergo electrochemical reactions in liquid water, forming metal cations such as zinc, aluminum, and magnesium. Magnesium ions, when present in aqueous solution, combine with the hydroxide ions produced by the electrochemical reaction to form a precipitated film primarily composed of magnesium hydroxide. This film appears black.

[0048] At the same time, zinc, aluminum, and magnesium ions can also combine with anions such as carbon dioxide dissolved in water to form compounds such as basic carbonates, which typically appear white. The formation of different compounds gives the zinc-aluminum-magnesium coating a different color. To prevent the zinc-aluminum-magnesium coating from turning black, it is essential to avoid the formation of a precipitated film primarily composed of magnesium hydroxide.

[0049] Zinc-aluminum-magnesium coatings typically form an initial solidification structure and a fine eutectic structure. Mg primarily exists in the eutectic structure as a compound, typically less than 10 microns in size and exhibiting high electrochemical activity. Al and Zn, on the other hand, often exist as an initial solidification structure or as a binary eutectic structure, which is coarser in size and therefore less electrochemically active. Mg compounds also have the lowest corrosion potential and are prone to electrochemical reactions, resulting in a precipitated film primarily composed of magnesium hydroxide.

[0050] Therefore, at least 80% of the eutectic surface area is occupied by grains with a surface size of no more than 100 μm. This means that the Al and Zn in the eutectic form fine grains, which can increase the electrochemical reaction rate of Al and Zn, making the reaction rates of Al, Mg, and Zn converge. This can quickly form compounds such as white basic carbonates containing Al, Mg, and Zn, rather than just black magnesium hydroxide compounds, thus preventing surface blackening.

[0051] In some embodiments of the present application, the alloy is composed of the following elements in weight percentage: 1-4% Al, 1-4% Mg, 0.0005-0.0020% rare earth elements, and 92-98% Zn.

[0052] In a second aspect, an embodiment of the present application provides a method for preparing an alloy, comprising the following steps:

[0053] S1: providing a substrate and a plating solution, wherein the elemental composition of the plating solution is exactly the same as that of the aforementioned alloy;

[0054] S2: hot-dip plating the alloy on the substrate using the plating solution.

[0055] Those skilled in the art will appreciate that there are many ways to form alloys. The alloys provided herein are primarily used in the field of coatings, where they exhibit excellent results. Furthermore, it is necessary to precipitate the compound particles formed by the rare earth elements before the initial solidification phase forms. Therefore, the alloys provided herein are prepared by hot-dip plating. The alloy preparation method provided herein can form a coating directly on a substrate.

[0056] In a third aspect, an embodiment of the present application provides an alloy coating, wherein the material of the alloy coating is the aforementioned alloy. The specific implementation of the alloy has been fully disclosed above and will not be repeated here.

[0057] Fourthly, embodiments of the present application provide a coated steel plate, comprising a steel plate substrate and a coating disposed on the steel plate substrate, wherein the coating is the aforementioned alloy coating. The specific implementation of the coating has been fully disclosed above and will not be repeated here.

[0058] In some embodiments of the present application, the surface roughness Ra of the steel plate substrate is in the range of 0.8 to 1.8 microns, and the peak number RPc is not less than 80.

[0059] Those skilled in the art will understand that the surface roughness morphology of the steel plate substrate can provide nucleation sites for the grain growth of the zinc-aluminum-magnesium coating during the hot-dip coating process, thereby refining the grains, improving the blackening resistance, and reducing the friction factor. In order to obtain sufficient nucleation growth sites, the number of peaks RPc on the substrate surface is required to be no less than 80; if the roughness Ra of the steel plate substrate surface is too small, the nucleation site will be too small and will not be able to play the role of a nucleation core, thereby weakening the effect of refining the grains. However, if the roughness Ra is too large, nucleation occurs at the bottom of the roughness morphology, and nucleation cannot occur at the top position of the roughness morphology, which will result in huge differences in grain size in the formed zinc-aluminum-magnesium coating, which is also not conducive to maintaining a low friction factor while improving the blackening resistance. Therefore, the surface roughness Ra of the substrate is required to be in the range of 0.8 to 1.8 μm.

[0060] In a fifth aspect, the present application further provides a method for preparing a coated steel plate, comprising the following steps:

[0061] Provide steel plate substrate;

[0062] An alloy coating is prepared on the surface of the steel plate substrate by the alloy preparation method described in this application to obtain a steel plate with a coating.

[0063] In some embodiments of the present application, the surface roughness Ra of the steel plate substrate reaches 0.8-1.8 μm, and the peak number RPc is not less than 80.

[0064] 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 generally 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 the conditions recommended by the manufacturer.

[0065] First, Table 1 is provided. Table 1 records the elemental composition, structural characteristics, and surface roughness of the steel plate substrate of the alloy coatings of Examples 1-7 and Comparative Examples 1-5.

[0066]

[0067]

[0068] Table 1

[0069] In Table 1, rare earth refers to either La or Ce, or a mixture of the two elements in any proportion. Since La and Ce have very similar atomic masses and chemical properties, their effects on the coating properties are not significantly different. Therefore, the mixing ratio of La and Ce has no significant effect on the properties of the coating, and the content of the rare earth elements is discussed uniformly in this application.

[0070] In Table 1, A represents the area ratio of the micro-solidified phase not larger than 100 μm on the surface of the initial solidified phase, B represents the area ratio of the grains not larger than 100 μm on the surface of the eutectic structure, and size represents the maximum size of the zinc compound particles containing rare earth elements.

[0071] In Table 1, Ra is the average surface roughness of the steel plate substrate, and RPc is the peak surface roughness of the steel plate substrate.

[0072] Example 1

[0073] This embodiment provides a steel plate with an alloy coating, including a steel plate substrate and an alloy coating coated on the surface of the steel plate substrate.

[0074] The average value Ra and peak value RPc of the surface roughness of the steel plate substrate are shown in Table 1.

[0075] The content of each element in the alloy coating is shown in Table 1.

[0076] The structural characteristics of the alloy coating, including the proportion of eutectic structure not larger than 100 μm, the proportion of initial solidification phase not larger than 100 μm, and the maximum size of zinc compound particles containing rare earth elements, are all recorded in Table 1.

[0077] This embodiment also provides a method for preparing the steel plate with the alloy coating, comprising the following steps:

[0078] Sa: providing a steel plate substrate, the surface roughness average value Ra and peak value RPc of the steel plate substrate are shown in Table 1;

[0079] Sb: providing a plating solution at a temperature of 400° C., wherein the elemental composition of the plating solution is completely identical to the elemental composition of the alloy coating;

[0080] Sc: After the temperature of the steel plate substrate is controlled to be the same as that of the plating solution, it is immersed in the plating solution and hot-dip coated for 5 seconds;

[0081] Sd: The steel plate substrate is removed and cooled to room temperature to obtain a steel plate with an alloy coating.

[0082] Hot dip coating is carried out in the following manner:

[0083] Example 2

[0084] The differences between this embodiment and embodiment 1 are shown in Table 1.

[0085] Example 3

[0086] The differences between this embodiment and embodiment 1 are shown in Table 1.

[0087] Example 4

[0088] The differences between this embodiment and embodiment 1 are shown in Table 1.

[0089] Example 5

[0090] The differences between this embodiment and embodiment 1 are shown in Table 1.

[0091] Example 6

[0092] The differences between this embodiment and embodiment 1 are shown in Table 1.

[0093] Example 7

[0094] The differences between this embodiment and embodiment 1 are shown in Table 1.

[0095] Comparative Example 1

[0096] The differences between this comparative example and Example 1 are shown in Table 1.

[0097] Comparative Example 2

[0098] The differences between this comparative example and Example 1 are shown in Table 1.

[0099] Comparative Example 3

[0100] The differences between this comparative example and Example 1 are shown in Table 1.

[0101] Comparative Example 4

[0102] The differences between this comparative example and Example 1 are shown in Table 1.

[0103] Comparative Example 5

[0104] The differences between this comparative example and Example 1 are shown in Table 1.

[0105] As can be seen from Table 1, due to the differences in elemental composition, the ratios of the various components in Comparative Example 1 exceed the preferred ranges of this application. Compared to Comparative Example 1, Examples 1-7 have a higher proportion of eutectic structures no larger than 100 μm, a higher proportion of initially solidified phases no larger than 100 μm, and a smaller maximum size of zinc compound particles containing rare earth elements. This demonstrates that the elemental composition design of Examples 1-5 can effectively increase the proportion of eutectic structures no larger than 100 μm and the proportion of initially solidified phases no larger than 100 μm, while reducing the maximum size of zinc compound particles containing rare earth elements.

[0106] Since no rare earth elements were added to Comparative Examples 2-3, Examples 1-7 had a higher proportion of eutectic structures no larger than 100 μm and a higher proportion of initially solidified phases no larger than 100 μm compared to Comparative Examples 2-3. This indicates that the addition of rare earth elements effectively increased the proportion of eutectic structures no larger than 100 μm and the proportion of initially solidified phases no larger than 100 μm.

[0107] The alloy compositions of Example 1 and Comparative Example 4 are identical, and the alloy compositions of Example 2 and Comparative Example 5 are identical. Because the Ra and RPc values of the steel substrates used in Comparative Examples 4-5 exceed the preferred ranges of this application, Examples 1-2 exhibit a higher proportion of eutectic structures no larger than 100 μm, a higher proportion of initially solidified phases no larger than 100 μm, and a smaller maximum size of zinc compound particles containing rare earth elements compared to Comparative Examples 4-5. This indicates that the Ra and RPc values of the steel substrates in Examples 1-5 are beneficial for increasing the proportion of eutectic structures no larger than 100 μm, the proportion of initially solidified phases no larger than 100 μm, and reducing the maximum size of zinc compound particles containing rare earth elements.

[0108] The steel plates with alloy coatings provided in Examples 1-7 and Comparative Examples 1-5 were subjected to blackening tests and surface deformation morphology tests. The test results are recorded in Table 2.

[0109] The blackening test is performed as follows:

[0110] The steel plate with the alloy coating was immersed in an acidic solution with a pH value of 5 for 60 seconds;

[0111] Rinse with deionized water;

[0112] Drying with dry air flow;

[0113] The surface brightness of the zinc-aluminum-magnesium coated steel sheet is measured as L0;

[0114] The samples were then placed in a hot and humid environment with an ambient temperature of 50°C and a relative humidity of 90% for 120 hours;

[0115] Measure the surface brightness L1;

[0116] Subtract L1 from L0 to obtain the brightness change ΔL. The larger the ΔL, the more serious the tendency of the coating to blacken.

[0117] The surface deformation morphology test is carried out as follows:

[0118] The steel plate with alloy coating was processed into a square plate sample of 250 mm × 250 mm;

[0119] Place the square plate sample in the center of the punch die. The diameter of the circular convex head of the die is 100mm, the radius of the corner is 2mm, and the diameter of the circular die is 110mm.

[0120] Clamp the square plate sample and punch the sample at a speed of 50 mm / min so that the deformation of the central part of the sample reaches 5%;

[0121] Remove the sample and observe the surface smoothness of the sample;

[0122] In Table 2, a surface having no visible unevenness was marked as ●, a surface having slight unevenness was marked as ○, and a surface having obvious visible unevenness was marked as ×.

[0123] Below, Table 2 is provided.

[0124] Surface smoothness ΔL Example 1 ● 1.2 Example 2 ● 2.3 Example 3 ● 2.8 Example 4 ● 3.5 Example 5 ● 4.1 Example 6 ● 3.8 Example 7 ● 1.8 Comparative Example 1 ○ 8.9 Comparative Example 2 × 8.7 Comparative Example 3 ○ 7.8 Comparative Example 4 ○ 6.8 Comparative Example 5 ○ 6.8

[0125] As shown in Table 2, after deformation of 5%, the surfaces of Examples 1-7 showed no visible unevenness, while Examples 1-5 exhibited slight or significant unevenness. This indicates that the alloy coatings of Examples 1-7 effectively overcome the problem of surface roughness after deformation. Surface smoothness is primarily positively correlated with the proportion of initially solidified phases no larger than 100 μm.

[0126] As shown in Table 2, the overall ΔL values of Examples 1-7 are significantly lower than those of Comparative Examples 1-5. This indicates that the alloy coatings of Examples 1-7 effectively overcome the blackening problem. ΔL is primarily positively correlated with the proportion of eutectic structures no larger than 100 μm.

[0127] Figure 2 The surface morphology of the alloy coating in Example 1 is shown; Figure 3 The surface morphology of the alloy coating in Comparative Example 3 is shown. Figure 2 、 Figure 3 It can be seen that the size of the initial solidified phase of the alloy coating in Example 1 is significantly smaller than that in Comparative Example 3.

[0128] 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 coated steel plate, characterized in that: The coated steel plate includes a steel plate substrate and a coating provided on the steel plate substrate, the coating being formed by hot-dip plating on the steel plate substrate with a plating solution, the plating solution including the following elements in weight percentage: 1-4% Al, 1-4% Mg, 0.0005-0.0020% rare earth elements, and 92-98% Zn; the rare earth element is at least one of La and Ce; the coating surface includes an initial solidification phase and a eutectic structure, at least 80% of the surface area of the initial solidification phase is occupied by a micro-solidification phase having a surface size not greater than 100 μm, the eutectic structure is a eutectic structure of Zn, Al, and Mg-Zn compounds, at least 80% of the surface area of the eutectic structure is occupied by grains having a surface size not greater than 100 μm, the surface roughness Ra of the steel plate substrate is in the range of 0.8 to 1.8 microns, and the peak number RPc is not less than 80.

2. The steel plate according to claim 1, wherein The coating comprises zinc compound particles containing rare earth.

3. The steel plate according to claim 2, characterized in that The diameter of the particles is no greater than 5 μm.

4. The steel plate according to claim 1, wherein The Mg-Zn compound includes MgZn2 and Mg2Zn 11 At least one of .

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