Easily degreased zinc-aluminum-magnesium coated steel plate and preparation method thereof

Abstract

The invention relates to an easily degreased zinc-aluminum-magnesium coated steel plate and a preparation method thereof, and belongs to the technical field of steel hot dipping treatment. The coated steel plate comprises a steel base body and a zinc-aluminum-magnesium coating attached to at least part of the surface of the steel base body. Wherein the ratio of the surface average roughness Ra of the zinc-aluminum-magnesium coating to the maximum roughness depth Rv of the zinc-aluminum-magnesium coating is less than or equal to 0.5; the contour bearing length rate Rmr of the zinc-aluminum-magnesium coating is larger than or equal to 70%. By optimizing the microstructure of the surface of the plating layer, a plurality of flat high points and a few deeper low points are formed on the surface of the plating layer, the few low points can ensure that the adsorption capacity of oil molecules on the surface of the plating layer is reduced, the wettability of water molecules on the surface is improved through the plurality of flat high points, and therefore good degreasing performance is achieved.

Description

Technical Field

[0001] This application relates to the technical field of hot-dip treatment of steel, and particularly to a zinc-aluminum-magnesium coated steel sheet that is easy to degrease and a preparation method thereof. Background Art

[0002] Hot-dip zinc treatment is an important surface treatment technology. It forms a firm metallurgical bonding coating on the surface of the steel substrate by reacting molten zinc and its alloys with the steel substrate. This hot-dip zinc-treated steel has been widely used in many industrial fields due to its unique performance advantages, such as strong coating adhesion, good corrosion resistance, long service life, relatively simple manufacturing process, and low product price. Moreover, its demand shows an increasing trend in many different industrial fields, especially in the automotive industry, electrical industry, and construction industry.

[0003] Currently, the commonly used hot-dip zinc coating is a zinc-aluminum-magnesium coating. The zinc-aluminum-magnesium coating combines the advantages of zinc, aluminum, and magnesium elements, further enhancing the corrosion resistance and service life of the coating. However, the zinc-aluminum-magnesium coating also presents certain challenges. In particular, the aluminum and magnesium elements on the surface of the coating are prone to react with oxygen in the air, forming a dense and fine oxide film. This oxide film not only has a strong polarity but also easily adsorbs polar oil molecules. This adsorption makes it difficult for the oil molecules to be effectively removed by subsequent degreasing solutions, thus bringing great difficulties to the degreasing treatment of the coated steel sheet. Degreasing treatment is an important step in the subsequent treatment of the steel sheet surface. Especially in industries such as automotive and household appliances, the coated steel sheet often needs to be subjected to phosphating and electrophoretic coating treatments to meet the high requirements for the surface quality and corrosion resistance of the steel sheet. However, due to the presence of the oxide film on the surface of the zinc-aluminum-magnesium coating, traditional degreasing methods are difficult to achieve an ideal cleaning effect, thus affecting the progress of subsequent treatments and the quality of the final product. Summary of the Invention

[0004] This application provides a zinc-aluminum-magnesium coated steel sheet that is easy to degrease and a preparation method thereof to solve the following technical problem: how to improve the degreasing performance of the zinc-aluminum-magnesium coating.

[0005] In a first aspect, an embodiment of this application provides a zinc-aluminum-magnesium coated steel sheet that is easy to degrease. The coated steel sheet includes a steel substrate and a zinc-aluminum-magnesium coating attached to at least a part of the surface of the steel substrate. Among them, the ratio of the average surface roughness Ra to the maximum roughness depth Rv of the zinc-aluminum-magnesium coating ≤ 0.5; the profile bearing length ratio Rmr of the zinc-aluminum-magnesium coating ≥ 70%.

[0006] Optionally, the surface magnesium oxide coverage rate of the zinc-aluminum-magnesium coating ≤ 50%.

[0007] Optionally, the average surface roughness Ra of the zinc-aluminum-magnesium coating ≤ 1 μm.

[0008] Optionally, in terms of mass fraction, the chemical composition of the zinc-aluminum-magnesium coating includes: Mg ≤ 1.5%, Al, and the matrix element Zn.

[0009] In a second aspect, an embodiment of the present application provides a method for preparing a zinc-aluminum-magnesium coated steel sheet that is easy to degrease as described in the first aspect. The method includes:

[0010] Hot dip plating the steel substrate to obtain a semi-finished zinc-aluminum-magnesium coated steel sheet;

[0011] Cooling, rolling, surface treatment, and coiling the semi-finished zinc-aluminum-magnesium coated steel sheet in sequence to obtain a zinc-aluminum-magnesium coated steel sheet.

[0012] Optionally, the cooling is carried out in a non-oxidizing atmosphere.

[0013] Optionally, the dew point temperature of the non-oxidizing atmosphere ≤ -50°C.

[0014] Optionally, the average surface roughness of the rolling rolls ≤ 2.0 μm.

[0015] Optionally, the elongation of the rolling material ≥ 1.0%.

[0016] Optionally, the surface treatment includes: soaking the rolled zinc-aluminum-magnesium coated steel sheet in a non-oxidizing acid solution with a pH of 4 to 6 for 1 s to 5 s.

[0017] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0018] An embodiment of the present application provides a zinc-aluminum-magnesium coated steel sheet that is easy to degrease. The coated steel sheet includes a steel substrate and a zinc-aluminum-magnesium coating attached to at least a part of the surface of the steel substrate. Among them, the ratio of the average surface roughness Ra to the maximum roughness depth Rv of the zinc-aluminum-magnesium coating ≤ 0.5; the profile bearing length ratio Rmr of the zinc-aluminum-magnesium coating ≥ 70%. By optimizing the surface microstructure of the coating, more flat high points and fewer deeper low points are formed on the coating surface. The few low points can ensure a decrease in the adsorption ability of oil molecules on the coating surface, while the more flat high points improve the wettability of water molecules on the surface, thereby achieving good degreasing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings here are incorporated into the description and form a part of this description, showing embodiments that conform to the present application, and are used together with the description to explain the principles of the present application.

[0020] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 It is a schematic flow chart of a preparation method of a zinc-aluminum-magnesium coated steel sheet that is easy to degrease provided by an embodiment of the present application. Detailed implementation manners

[0022] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts fall within the scope of protection of the present application.

[0023] The various embodiments of the present application may exist 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 construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and individual values within that range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within that range, such as 1, 2, 3, 4, 5, and 6, which applies regardless of the range; additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0024] In this text, terms such as "including" mean "including but not limited to". Relative 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 associated relationship of associated objects and indicates that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, or B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "multiple" means two or more; "at least one kind", "at least one of the following (items)" or similar expressions refer to any combination of these items, including any combination of single items (pieces) or plural items (pieces); for example, "at least one of a, b, or c", or "at least one of a, b, and c" can both mean: a, b, c, a-b (that is, a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple respectively. "Parts representation method" such as parts by weight, parts by mass, etc. represents the proportional relationship between each component. In the proportional relationships involved in this text, the parameters that need to be described by proportions should be understood as the antecedents of the proportional formula in the order of description, and the proportional numbers should be understood as the consequents of the proportional formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportional formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0025] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in this text can be obtained through market purchase or can be prepared by existing methods.

[0026] In a first aspect, an embodiment of the present application provides a zinc-aluminum-magnesium coated steel sheet that is easily degreased. The coated steel sheet includes a steel substrate and a zinc-aluminum-magnesium coating attached to at least a part of the surface of the steel substrate; wherein, the ratio of the average surface roughness Ra of the zinc-aluminum-magnesium coating to the maximum roughness depth Rv of the zinc-aluminum-magnesium coating ≤ 0.5; the profile support length rate Rmr of the zinc-aluminum-magnesium coating ≥ 70%.

[0027] The zinc-aluminum-magnesium coated steel sheet of the embodiment of the present application includes a steel substrate and a zinc-aluminum-magnesium coating attached to at least a part of the surface of the steel substrate. There is no special limitation on the steel substrate, and ordinary steel sheets such as hot-rolled steel sheets and cold-rolled steel sheets can be used. There is also no special limitation on the steel grade, and for example, aluminum-killed steel, extra-low-carbon steel, and high-strength steel can be used.

[0028] The zinc-aluminum-magnesium coating is formed on the surface of the steel substrate. The mass percentage of element Zn in this coating exceeds 50%, and the rest are element Al and element Mg. Element Mg is very active in the air and is easily oxidized to form a magnesium oxide film on the surface. The magnesium oxide film is a compound with a very strong polarity, which easily adsorbs polar oil molecules. At the same time, it makes it difficult for the degreasing liquid to wet the coating surface, making it difficult for the oil molecules to be wrapped by the emulsifier and active molecular groups of the degreasing liquid, thus resulting in a decrease in the surface degreasing efficiency of the zinc-aluminum-magnesium coating. Therefore, the main direction to improve the poor degreasing of the zinc-aluminum-magnesium coating is to improve the wettability of the zinc-aluminum-magnesium coating to the degreasing liquid and reduce the adsorption of the zinc-aluminum-magnesium coating to oil molecules.

[0029] The surface average roughness Ra refers to the arithmetic mean of the absolute values of the profile offsets within the sampling length, which reflects the magnitude of the microscopic geometric shape error of the coating surface. The surface average roughness Ra is usually measured using a surface roughness measuring instrument (such as a profilometer). During measurement, the instrument scans along a straight line on the coating surface and records the surface profile data. Then, based on these data, the surface average roughness Ra is calculated. The maximum roughness depth Rv refers to the maximum value of the distance between the profile peak line and the profile valley bottom line within the sampling length, which directly reflects the most uneven part of the coating surface. The smaller the Ra / Rv of the coating surface, the more flat high points and fewer deep low points are formed on the coating surface. Fewer low points can ensure a decrease in the adsorption ability of oil molecules on the coating surface, while more flat high points improve the wettability of water molecules on the surface. Exemplarily, the ratio of the surface average roughness Ra to the maximum roughness depth Rv of the coating can be 0.1, 0.2, 0.3, 0.4, 0.5, etc.

[0030] Rmr (profile bearing length ratio) is the ratio of the profile bearing length to the sampling length and is used to describe the shape characteristics of the surface roughness. A higher Rmr parameter also indicates that more flat high points and fewer deep low points are formed on the coating surface. Exemplarily, the Rmr of the coating can be 70%, 73%, 76%, 79%, 82%, 85%, etc.

[0031] In some embodiments, the surface magnesium oxide coverage rate of the zinc-aluminum-magnesium coating ≤ 50%.

[0032] Since the magnesium oxide film on the surface of the zinc-aluminum-magnesium coating has a negative impact on the degreasing performance of the coating, the magnesium oxide film on the surface of the zinc-aluminum-magnesium coating should be minimized. In the embodiments of this application, the coverage rate of the magnesium oxide film on the surface of the zinc-aluminum-magnesium coating does not exceed 50%. Exemplarily, the surface magnesium oxide coverage rate of the zinc-aluminum-magnesium coating can be 10%, 20%, 30%, 40%, 50%, etc.

[0033] In some embodiments, the surface average roughness Ra of the zinc-aluminum-magnesium coating ≤ 1 μm.

[0034] The microstructure of the coating has a direct and obvious impact on the wetting behavior of the degreasing solution on the coating surface. It has been found that if the surface roughness Ra of the coating is small, the wettability of the degreasing solution on the coating surface can be improved. In the embodiments of the present application, it is required that the average surface roughness of the coating is not greater than 1 μm. Exemplarily, the average surface roughness Ra of the zinc-aluminum-magnesium coating can be 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, etc.

[0035] In some embodiments, in terms of mass fraction, the chemical composition of the zinc-aluminum-magnesium coating includes: Mg ≤ 1.5%, Al, and the matrix element Zn.

[0036] In terms of composition design, in the embodiments of the present application, it is required that the mass percentage of element Mg in the zinc-aluminum-magnesium coating does not exceed 1.5%. By reducing element Mg, the coverage rate of the magnesium oxide film on the coating surface can be effectively reduced. However, element Mg in the zinc-aluminum-magnesium coating cannot be reduced infinitely because magnesium provides excellent corrosion resistance, which is the main advantage of the zinc-aluminum-magnesium coating. Generally speaking, the mass percentage of magnesium element in the zinc-aluminum-magnesium coating should not be lower than 0.8% to ensure its corrosion resistance. Exemplarily, the mass fraction of Mg in the zinc-aluminum-magnesium coating can be 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.

[0037] Figure 1 It is a schematic flow chart of a method for preparing a zinc-aluminum-magnesium coated steel sheet with easy degreasing provided by the embodiments of the present application.

[0038] Please refer to Figure 1 , secondly, the embodiments of the present application provide a method for preparing the zinc-aluminum-magnesium coated steel sheet with easy degreasing described in the first aspect, and the method includes:

[0039] S1. Hot dip coat the steel substrate to obtain a semi-finished zinc-aluminum-magnesium coated steel sheet;

[0040] Through the hot dip coating technology, a zinc-aluminum-magnesium alloy coating is covered on the surface of the steel substrate.

[0041] S2. Cool, roll, perform surface treatment and coil the semi-finished zinc-aluminum-magnesium coated steel sheet in sequence to obtain a zinc-aluminum-magnesium coated steel sheet.

[0042] Cooling, rolling, surface treatment and coiling are processes for further processing and improving the coated steel sheet.

[0043] The rolling process can adjust the thickness and shape of the steel sheet. Through surface treatment, dirt and grease on the steel sheet surface can be removed, the degreasing performance and surface quality of the steel sheet can be improved, and coiling is convenient for subsequent storage and transportation.

[0044] In some embodiments, the cooling is carried out in a non-oxidizing atmosphere.

[0045] In addition to reducing the element Mg during the coating composition design, the manufacturing process can also be optimized to achieve the purpose of reducing the magnesium oxide film. Using a non-oxidizing atmosphere for protection in the cooling section after hot-dip coating can prevent the zinc-aluminum-magnesium coating from rapidly oxidizing at high temperatures to form a magnesium oxide film with a coverage rate exceeding 50% and being loose. The loose magnesium oxide film contains a large number of oxide pores, increasing the specific surface area of the oxide, and the true coverage rate of the oxide can even exceed 100%.

[0046] Adopting a cooling process protected by a non-oxidizing atmosphere, such as nitrogen, can prevent the zinc-aluminum-magnesium coated steel plate from contacting oxygen molecules as much as possible during the cooling process, thereby avoiding the formation of a loose magnesium oxide film at high temperatures. In addition to using nitrogen for protection, other non-oxidizing gases, such as argon, helium, etc., can also be used.

[0047] In some embodiments, the dew point temperature of the non-oxidizing atmosphere is ≤ -50°C.

[0048] Although the non-oxidizing atmosphere itself has no oxidation effect, there may be a certain amount of residual water molecules in it. Water molecules have a strong oxidation effect at high temperatures. Therefore, it is necessary to control the content of residual water molecules in the non-oxidizing atmosphere. The water molecule content is usually expressed by the dew point temperature. The higher the dew point temperature, the higher the water molecule content. In the embodiments of the present application, it is required that the dew point temperature of the non-oxidizing atmosphere does not exceed -50°C. Exemplarily, the dew point temperature of the non-oxidizing atmosphere can be -50°C, -52°C, -54°C, -56°C, -58°C, -60°C, etc.

[0049] In some embodiments, the average surface roughness of the rolling roll is ≤ 2.0 μm.

[0050] After the coating solidifies, the coated steel plate needs to be rolled to reduce the coverage rate of the magnesium oxide film. However, rolling usually causes an increase in the roughness Ra and a decrease in Rmr of the coating. Therefore, it is necessary to specify the surface topography of the roll used during rolling. Using a roll with a smaller roughness can prevent the Ra of the coating surface from rising too high. In the embodiments of the present application, it is required that the roughness of the roll does not exceed 2.0 μm. Exemplarily, the average surface roughness of the roll can be 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, etc.

[0051] In some embodiments, the elongation of the rolling material is ≥ 1.0%.

[0052] Rolling the cooled coated steel sheet can break the magnesium oxide film on the coating surface and reduce the coverage rate. Therefore, a relatively large rolling elongation is required during rolling to tear the magnesium oxide film. In the embodiments of the present application, the elongation of the rolled material is specified to be not less than 1.0%. Exemplarily, the elongation of the rolled material can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.

[0053] In some embodiments, the surface treatment includes: immersing the rolled zinc-aluminum-magnesium coated steel sheet in a non-oxidizing acid solution with a pH of 4 to 6 for 1 s to 5 s.

[0054] During the preparation of the zinc-aluminum-magnesium coated steel sheet, immersion treatment with a non-oxidizing acid solution can significantly reduce the magnesium oxide film on the surface of the zinc-aluminum-magnesium coating. The acid solution used must be a non-oxidizing acid solution, such as phosphoric acid, citric acid, hydrochloric acid, dilute sulfuric acid, etc. Magnesium oxide easily reacts with these non-oxidizing acid solutions. When the pH is not greater than 6, the reaction can proceed rapidly. Therefore, it is required that the pH of the acid solution cannot be greater than 6; however, if the pH of the acid solution is too low, the coating body will be corroded to form pit points, which will absorb oil molecules, resulting in poor degreasing. At the same time, the pit points will cause the coating to become thinner and weaken the corrosion resistance of the coating. Therefore, in the embodiments of the present application, the pH of the acid solution cannot be less than 4. Exemplarily, the pH of the non-oxidizing acid solution can be 4, 4.5, 5, 5.5, 6, etc.

[0055] The time of the acid pickling treatment also needs to be controlled. If the time is too short, the effect of effectively eliminating magnesium oxide cannot be achieved. However, if the time is too long, pit points will appear on the coating surface due to corrosion. In the embodiments of the present application, the treatment time is specified to be 1 s to 5 s. Exemplarily, the time of acid pickling can be 1 s, 2 s, 3 s, 4 s, 5 s, etc.

[0056] The preparation product of the preparation method of the easily degreased zinc-aluminum-magnesium coated steel sheet is the above-mentioned easily degreased zinc-aluminum-magnesium coated steel sheet. Since the preparation method of the easily degreased zinc-aluminum-magnesium coated steel sheet adopts some or all of the technical solutions of the embodiments of the easily degreased zinc-aluminum-magnesium coated steel sheet, it at least has all the beneficial effects brought by the technical solutions of the easily degreased zinc-aluminum-magnesium coated steel sheet, which will not be elaborated one by one here.

[0057] The following further elaborates the present application in conjunction with specific embodiments. For the experimental methods without specific conditions noted in the following embodiments, they are usually determined in accordance with national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out in accordance with general international standards, conventional conditions or the conditions recommended by the manufacturer.

[0058] A steel plate with a thickness of 1.0 mm and a width of 1500 mm is used as the substrate, and the coating weight is 100 grams per square meter on both sides. The characteristics of Examples 1-13 and Comparative Examples 1-5 of this application are shown in Table 1.

[0059] Use a surface profiler to detect the roughness parameters of the coating surface, including Rmr, Ra, and Rv. Use ICP technology to analyze the Mg element content in the coating.

[0060] Use electron probe technology to analyze the magnesium and oxygen elements on the coating surface. The surface with a magnesium element content exceeding 3.0% and an oxygen element content exceeding 20% is defined as the magnesium oxide covered area. Use image recognition technology to count the proportion of the magnesium oxide covered area in the entire analyzed surface area of the sample piece as the coverage rate of magnesium oxide.

[0061] Table 1

[0062]

[0063]

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

[0065] Table 2

[0066]

[0067] Carry out a degreasing performance corrosion evaluation experiment on the zinc-aluminum-magnesium coated steel plates prepared in the above Examples 1-13 and Comparative Examples 1-5: Coat a layer of wax-free rust preventive oil on the surface of the zinc-aluminum-magnesium coated steel plate, and the coating weight of the rust preventive oil is 1 g / m 2 . Let it stand for 24 hours to allow the oil molecules to fully contact the coating. Then place the zinc-aluminum-magnesium coated steel plate into a sodium hydroxide aqueous solution with a pH of 14, and the temperature of the aqueous solution is 50 °C, which is prepared with deionized water. Immerse it for 10 minutes. Continuously stir the sodium hydroxide aqueous solution during the immersion process. Then take out the zinc-aluminum-magnesium coated steel plate and rinse the surface with sodium hydroxide solution, and the rinsing water flow rate is 0.2 - 1.0 m / s. Then clean the surface of the zinc-aluminum-magnesium coating with deionized water. Observe the water film state on the surface of the zinc-aluminum-magnesium coated steel plate after cleaning. If the water film can completely cover the surface of the zinc-aluminum-magnesium coating, the degreasing is excellent (√). If the water film can only cover less than 100% but not less than 95% of the surface of the zinc-aluminum-magnesium coating, the degreasing is good (▲), and if the water film coverage rate is less than 95%, the degreasing is poor (×).

[0068] The corrosion resistance test was carried out on the zinc-aluminum-magnesium coated steel sheets prepared in the above Examples 1-13 and Comparative Examples 1-5: The surface of the zinc-aluminum-magnesium coated steel sheets was degreased, phosphated and electrophoresed, and an electrophoretic film with a thickness of 10-15 microns was coated on the surface. Then, a scratch was made on the surface of the electrophoretic film with a tool, the width of the scratch was 0.8 mm, and the depth of the scratch reached the surface of the coating. The treated zinc-aluminum-magnesium coated steel sheets were placed in a cyclic corrosion test chamber, and the corrosion test was carried out using the cyclic corrosion test method of PV 1210 standard. The corrosion test was carried out for 6 weeks. Then, the zinc-aluminum-magnesium coated steel sheets were taken out, and the width of the corrosion expansion of the paint film near the scratch was measured. If the unilateral expansion width does not exceed 3 mm, the corrosion resistance is excellent (√). If the unilateral expansion width exceeds 3 mm but is less than 4 mm, the corrosion resistance is good (▲). If the unilateral expansion width exceeds 4 mm, the corrosion resistance is poor (×).

[0069] The experimental evaluation results are shown in Table 3 below.

[0070] Table 3

[0071]

[0072]

[0073] As can be seen from Tables 1 to 3, in Examples 1 to 13, the chemical composition and characteristics of the zinc-aluminum-magnesium coating are all within the required ranges of the present invention, and the coating surface has excellent degreasing performance.

[0074] One or more technical solutions in the embodiments of the present invention at least further have the following technical effects or advantages:

[0075] The preparation method provided by the embodiments of the present invention has the effects of being simple and easy to operate, having low production cost, and being easy to promote and use.

[0076] The above are only specific embodiments of the present application, which enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, 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 these embodiments shown in the present application, but will conform to the widest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A zinc-aluminum-magnesium coated steel sheet that is easy to degrease, said coated steel sheet comprising a steel substrate and a zinc-aluminum-magnesium coating adhered to at least a part of the surface of said steel substrate; Among them, The ratio of the average surface roughness Ra of the zinc-aluminum-magnesium coating to the maximum roughness depth Rv of the zinc-aluminum-magnesium coating ≤ 0.5; the profile bearing length ratio Rmr of the zinc-aluminum-magnesium coating ≥ 70%.

2. The coated steel sheet according to claim 1, wherein The surface magnesium oxide coverage rate of the zinc-aluminum-magnesium coating ≤ 50%.

3. The coated steel sheet according to claim 1, wherein The average surface roughness Ra of the zinc-aluminum-magnesium coating ≤ 1 μm.

4. The coated steel sheet according to claim 1, characterized in that, By mass fraction, the chemical composition of the zinc-aluminum-magnesium coating includes: Mg ≤ 1.5%, Al, and the matrix element Zn.

5. A preparation method of the zinc-aluminum-magnesium coated steel sheet that is easy to degrease according to any one of claims 1 to 4, said method comprising: Hot-dip plating the steel substrate to obtain a semi-finished zinc-aluminum-magnesium coated steel sheet; Cooling, rolling, surface treatment and coiling the semi-finished zinc-aluminum-magnesium coated steel sheet in sequence to obtain the zinc-aluminum-magnesium coated steel sheet.

6. The method according to claim 5, wherein The cooling is carried out in a non-oxidizing atmosphere.

7. The method according to claim 6, wherein The dew point temperature of the non-oxidizing atmosphere ≤ -50 °C.

8. The method according to claim 5, wherein The average surface roughness of the roll for the rolling ≤ 2.0 μm.

9. The method according to claim 5, characterized in that, The material elongation rate of the rolling ≥ 1.0%.

10. The method according to claim 5, wherein The surface treatment includes: soaking the rolled zinc-aluminum-magnesium coated steel sheet in a non-oxidizing acid solution with a pH of 4 to 6 for 1 s to 5 s.

Images