Blackening method for hot-dip Zn-AI-Mg series alloy coating

Abstract

The invention relates to the field of metal surface treatment, and discloses a blackening method for a hot-dip Zn-AI-Mg alloy plating layer, and the alloy plating layer comprises the following components in percentage by mass: 5.0-15.0 wt.% of Al, 2.0-4.0 wt.% of Mg, 0.1-0.3 wt.% of Si and the balance of Zn. According to the blackening method provided by the invention, vacuumizing is not needed, and the blackening time is shortened; the time can be saved to a great extent while the possibility of industrial production is improved, and the production cost is reduced; the alloy blackening coating obtained through the method is uniform in color, and the method is easy and convenient to operate.

Description

Technical Field

[0001] The invention relates to the field of metal surface treatment, in particular to a hot-dip Zn-Al-Mg alloy coating blackening method. Background Art

[0002] In today's industrial field, black surface treatment is highly favored due to its unique design aesthetics and functional advantages. The demand for black products in industries such as automobiles, construction and electronics has increased significantly, not only because it perfectly fits the modern and luxurious image, but also because of the practical performance of black surface in terms of heat absorption.

[0003] At present, the conventional method to achieve a black appearance is to coat the surface of the steel plate with black pigment after hot-dip galvanizing (Zn) or zinc-magnesium-aluminum (Zn-Al-Mg). However, this process has multiple technical limitations: on the one hand, the coating process increases the production cost and produces volatile organic compounds (VOCs) to cause environmental pollution; on the other hand, the coating will affect the implementation of subsequent forming processes such as welding. More importantly, relying solely on surface coating to achieve blackening is not only difficult to improve the overall performance of the product, but damage to the coating may also lead to a decrease in the corrosion resistance of the substrate. The existing method of blackening the surface of hot-dip galvanized (Zn) or zinc-magnesium-aluminum (Zn-Al-Mg) plates requires a high temperature, and a certain vacuum degree needs to be maintained during the experiment. The processing time is long and the entire experimental steps are relatively cumbersome. For this reason, this application proposes a hot-dip Zn-AI-Mg alloy coating blackening method. Summary of the invention

[0004] The object of the present invention is to provide a method for blackening a hot-dip Zn-Al-Mg alloy coating to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a hot-dip Zn-Al-Mg alloy coating, comprising the following components by mass percentage: Al 5.0-15.0wt.%, Mg 2.0-4.0wt.%, Si 0.1-0.3wt.%, and the remainder is Zn.

[0006] According to the above-mentioned hot-dip Zn-Al-Mg alloy coating blackening method, the following steps are included:

[0007] (1) hot-dip plating is performed on the pre-treated steel sheet in a plating tank, and then a series of post-treatments are performed to obtain a Zn-Al-Mg alloy plate;

[0008] (2) cutting the hot-dip Zn-Al-Mg alloy plate into specified sizes by electric spark cutting;

[0009] (3) ultrasonically clean the cut plates, rinse and dry them;

[0010] (4) placing the plate obtained in step (3) into a wet heat test chamber;

[0011] (5) The wet heat test chamber is set to a predetermined temperature, humidity and time, and a hot-dip Zn-Al-Mg alloy plate with a blackened surface can be obtained.

[0012] Preferably, the hot-dip coating temperature in step (1) is 430° C.-500° C., the hot-dip coating time is 2-10 s, and the thickness of the alloy coating is 10-60 μm.

[0013] Preferably, the size after electric spark cutting in step (2) is 15-16 cm in length, 10-11 cm in width and 0.8-0.9 mm in thickness.

[0014] Preferably, in step (3), the plate is ultrasonically treated in anhydrous ethanol, and after the ultrasonic treatment is completed, it is wiped with acetone and anhydrous ethanol, washed with deionized water and dried for later use.

[0015] Preferably, in step (3), the ultrasonic treatment time of anhydrous ethanol is 600 s, acetone is evenly dipped into an ultra-fine dust-free cloth and wiped on the surface of the coating for 12 min, then rinsed with deionized water and dried in an oven at 50° C. for 20 min.

[0016] Preferably: the humidity range of the heat and humidity test chamber used in the step (4) is 20% RH-100% RH, the temperature range is -20°C-150°C, the effective volume is ≥40L, the effective box inner dimensions are 350mm in diameter, 50mm in depth, the temperature fluctuation is ±0.3°C, the temperature uniformity is 3.0°C, the temperature deviation is ±3.0°C, the absolute pressure range is 100-300Kpa, and the pressure deviation is ±2Kpa.

[0017] Preferably, the experimental temperature in step (5) is 80°C-140°C, the experimental humidity is 60%RH-100%RH, the experimental time is 3h-10h, and the water source used for humidification is drinking purified water.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The alloy coating composition used in the present invention increases the Al content, improves the corrosion resistance of the coating, improves the high temperature performance, enhances the mechanical properties and also improves the surface quality; 2. The hot dip plating temperature is controlled at 430°C-500°C. Under this temperature range, the zinc liquid has suitable fluidity, which can promote the full mixing of Zn with Al and Mg elements. At the same time, this temperature range can avoid excessive oxidation of the substrate and ensure the good combination of the coating and the substrate; 3. The hot dip plating time is controlled at 2-10s. This time period can effectively inhibit excessive diffusion reaction and prevent the formation of an overly thick alloy layer. Short-time immersion plating can reduce the thermal impact of the substrate and reduce the risk of thermal deformation; 4. A treatment method for blackening the sample plate at a certain temperature, humidity and time using a wet heat test chamber does not require vacuuming during the treatment process, which reduces the production cost and increases the possibility of industrial production; 5. Compared with the existing blackening treatment method, the method of the present invention can save time to a great extent and reduce the time cost of production; 6. The alloy blackening coating produced by the method is uniform in color, and the method of the present invention is easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a flow chart of the method of the present invention;

[0021] Figure 2 This is a comparison chart of the experimental results. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] A hot-dip Zn-Al-Mg alloy coating comprises the following components by mass percentage: Al 5.0-15.0wt.%, Mg 2.0-4.0wt.%, Si 0.1-0.3wt.%, and the balance is Zn.

[0024] See also Figure 1 The method for blackening a hot-dip Zn-Al-Mg alloy coating shown in the figure comprises the following steps: (1) subjecting a pre-treated steel plate to a hot-dip coating process in a coating tank, and then subjecting the pre-treated steel plate to a series of post-treatments to obtain a Zn-Al-Mg alloy coating plate;

[0025] (2) cutting the hot-dip Zn-Al-Mg alloy plate into specified sizes by electric spark cutting;

[0026] (3) ultrasonically clean the cut plates, rinse and dry them;

[0027] (4) placing the plate obtained in step (3) into a wet heat test chamber;

[0028] (5) The wet heat test chamber is set to a predetermined temperature, humidity and time, and a hot-dip Zn-Al-Mg alloy plate with a blackened surface can be obtained.

[0029] Example 1

[0030] A method for blackening the surface of a hot-dip Zn-Al-Mg alloy coating, wherein the hot-dip Zn-Al-Mg alloy coating comprises the following components by mass percentage: Al 5.0-15.0wt.%, Mg 2.0-4.0wt.%, Si 0.1-0.3wt.%, and the balance is Zn. The blackening method comprises the following steps:

[0031] (1) The pretreated steel plate is subjected to a hot dip plating process in a plating tank, the hot dip plating temperature is 430°C-500°C, the hot dip plating time is 2-10s, and the desired hot dip Zn-Al-Mg alloy plate is obtained after post-treatment.

[0032] (2) The hot-dip Zn-Al-Mg alloy plate is cut by electric spark cutting into a length of 15-16 cm, a width of 10-11 cm, and a thickness of 0.8-0.9 mm.

[0033] (3) The cut plate section is polished and cleaned, ultrasonically treated in anhydrous ethanol for 600 seconds, and acetone is evenly dipped into an ultra-fine dust-free cloth and wiped on the coating surface for 1-2 minutes to further remove any organic pollutants that may exist on the coating surface. The plate is then rinsed with deionized water and dried in an oven at 50°C for 20 minutes to ensure that the surface moisture is completely evaporated.

[0034] (4) High temperature and high humidity treatment: The parameters of the wet heat test chamber used are as follows: humidity range is 20% RH-100% RH, temperature range is -20℃-150℃, effective volume ≥40L, effective box inner dimensions are 350mm in diameter and 50mm in depth, temperature fluctuation is ±0.3℃, temperature uniformity is 3.0℃, temperature deviation is ±3.0℃, absolute pressure range is 100-300Kpa, and pressure deviation is ±2Kpa.

[0035] (5) The experimental temperature was set to 110°C, the humidity was set to 90% RH, and the treatment time was set to 3 h, and the samples were subjected to high temperature and high humidity treatment.

[0036] Example 2

[0037] A method for blackening a hot-dip Zn-Al-Mg alloy coating, wherein the hot-dip Zn-Al-Mg alloy coating comprises the following components by mass percentage: Al 5.0-15.0wt.%, Mg 2.0-4.0wt.%, Si 0.1-0.3wt.%, and the balance is Zn, and the blackening method comprises the following steps:

[0038] (1) The pretreated steel plate is subjected to a hot dip plating process in a plating tank, the hot dip plating temperature is 430°C-500°C, the hot dip plating time is 2-10s, and the desired hot dip Zn-Al-Mg alloy plate is obtained after post-treatment.

[0039] (2) The hot-dip Zn-Al-Mg alloy plate is cut by electric spark cutting into a length of 15-16 cm, a width of 10-11 cm, and a thickness of 0.8-0.9 mm.

[0040] (3) The cut plate section is polished and cleaned, ultrasonically treated in anhydrous ethanol for 600 seconds, and acetone is evenly dipped into an ultra-fine dust-free cloth and wiped on the coating surface for 1-2 minutes to further remove any organic pollutants that may exist on the coating surface. The plate is then rinsed with deionized water and dried in an oven at 50°C for 20 minutes to ensure that the surface moisture is completely evaporated.

[0041] (4) High temperature and high humidity treatment: The parameters of the wet heat test chamber used are as follows: humidity range is 20% RH-100% RH, temperature range is -20℃-150℃, effective volume ≥40L, effective box inner dimensions are 350mm in diameter and 50mm in depth, temperature fluctuation is ±0.3℃, temperature uniformity is 3.0℃, temperature deviation is ±3.0℃, absolute pressure range is 100-300Kpa, and pressure deviation is ±2Kpa.

[0042] (5) The experimental temperature was set to 110°C, the humidity was set to 100% RH, and the treatment time was set to 3 h, and the samples were subjected to high temperature and high humidity treatment.

[0043] Example 3

[0044] A method for blackening the surface of a hot-dip Zn-Al-Mg alloy coating, wherein the hot-dip Zn-Al-Mg alloy coating comprises the following components by mass percentage: Al 5.0-15.0wt.%, Mg 2.0-4.0wt.%, Si 0.1-0.3wt.%, and the balance is Zn, and the blackening method comprises the following steps:

[0045] (1) The pretreated steel plate is subjected to a hot dip plating process in a plating tank, the hot dip plating temperature is 430°C-500°C, the hot dip plating time is 2-10s, and the desired hot dip Zn-Al-Mg alloy plate is obtained after post-treatment.

[0046] (2) The hot-dip Zn-Al-Mg alloy plate is cut by electric spark cutting into a length of 15-16 cm, a width of 10-11 cm, and a thickness of 0.8-0.9 mm.

[0047] (3) The cut plate section is polished and cleaned, ultrasonically treated in anhydrous ethanol for 600 seconds, and acetone is evenly dipped into an ultra-fine dust-free cloth and wiped on the coating surface for 1-2 minutes to further remove any organic pollutants that may exist on the coating surface. The plate is then rinsed with deionized water and dried in an oven at 50°C for 20 minutes to ensure that the surface moisture is completely evaporated.

[0048] (4) High temperature and high humidity treatment: The parameters of the wet heat test chamber used are as follows: humidity range is 20% RH-100% RH, temperature range is -20℃-150℃, effective volume ≥40L, effective box inner dimensions are 350mm in diameter and 50mm in depth, temperature fluctuation is ±0.3℃, temperature uniformity is 3.0℃, temperature deviation is ±3.0℃, absolute pressure range is 100-300Kpa, and pressure deviation is ±2Kpa.

[0049] (5) The experimental temperature was set to 120°C, the humidity was set to 90% RH, and the treatment time was set to 3 h, and the samples were subjected to high temperature and high humidity treatment.

[0050] Example 4

[0051] A method for blackening the surface of a hot-dip Zn-Al-Mg alloy coating, wherein the hot-dip Zn-Al-Mg alloy coating comprises the following components by mass percentage: Al 5.0-15.0wt.%, Mg 2.0-4.0wt.%, Si 0.1-0.3wt.%, and the balance is Zn, and the blackening method comprises the following steps:

[0052] (1) The pretreated steel plate is subjected to a hot dip plating process in a plating tank, the hot dip plating temperature is 430°C-500°C, the hot dip plating time is 2-10s, and the desired hot dip Zn-Al-Mg alloy plate is obtained after post-treatment.

[0053] (2) The hot-dip Zn-Al-Mg alloy plate is cut by electric spark cutting into a length of 15-16 cm, a width of 10-11 cm, and a thickness of 0.8-0.9 mm.

[0054] (3) The cut plate section is polished and cleaned, ultrasonically treated in anhydrous ethanol for 600 seconds, and acetone is evenly dipped into an ultra-fine dust-free cloth and wiped on the coating surface for 1-2 minutes to further remove any organic pollutants that may exist on the coating surface. The plate is then rinsed with deionized water and dried in an oven at 50°C for 20 minutes to ensure that the surface moisture is completely evaporated.

[0055] (4) High temperature and high humidity treatment: The parameters of the wet heat test chamber used are as follows: humidity range is 20% RH-100% RH, temperature range is -20℃-150℃, effective volume ≥40L, effective box inner dimensions are 350mm in diameter and 50mm in depth, temperature fluctuation is ±0.3℃, temperature uniformity is 3.0℃, temperature deviation is ±3.0℃, absolute pressure range is 100-300Kpa, and pressure deviation is ±2Kpa.

[0056] (5) The experimental temperature was set to 120°C, the humidity was set to 100% RH, and the treatment time was set to 3 h, and the samples were subjected to high temperature and high humidity treatment.

[0057] Example 5

[0058] A method for blackening the surface of a hot-dip Zn-Al-Mg alloy coating, wherein the hot-dip Zn-Al-Mg alloy coating comprises the following components by mass percentage: Al 5.0-15.0wt.%, Mg 2.0-4.0wt.%, Si 0.1-0.3wt.%, and the balance is Zn, and the blackening method comprises the following steps:

[0059] (1) The pretreated steel plate is subjected to a hot dip plating process in a plating tank, the hot dip plating temperature is 430°C-500°C, the hot dip plating time is 2-10s, and the desired hot dip Zn-Al-Mg alloy plate is obtained after post-treatment.

[0060] (2) The hot-dip Zn-Al-Mg alloy plate is cut by electric spark cutting into a length of 15-16 cm, a width of 10-11 cm, and a thickness of 0.8-0.9 mm.

[0061] (3) The cut plate section is polished and cleaned, ultrasonically treated in anhydrous ethanol for 600 seconds, and acetone is evenly dipped into an ultra-fine dust-free cloth and wiped on the coating surface for 1-2 minutes to further remove any organic pollutants that may exist on the coating surface. The plate is then rinsed with deionized water and dried in an oven at 50°C for 20 minutes to ensure that the surface moisture is completely evaporated.

[0062] (4) High temperature and high humidity treatment: The parameters of the wet heat test chamber used are as follows: humidity range is 20% RH-100% RH, temperature range is -20℃-150℃, effective volume ≥40L, effective box inner dimensions are 350mm in diameter and 50mm in depth, temperature fluctuation is ±0.3℃, temperature uniformity is 3.0℃, temperature deviation is ±3.0℃, absolute pressure range is 100-300Kpa, and pressure deviation is ±2Kpa.

[0063] (5) The experimental temperature was set to 120°C, the humidity was set to 100% RH, and the treatment time was set to 4.5 h, and the samples were subjected to high temperature and high humidity treatment.

[0064] Example 6

[0065] A method for blackening the surface of a hot-dip Zn-Al-Mg alloy coating, wherein the hot-dip Zn-Al-Mg alloy coating comprises the following components by mass percentage: Al 5.0-15.0wt.%, Mg 2.0-4.0wt.%, Si 0.1-0.3wt.%, and the balance is Zn, and the blackening method comprises the following steps:

[0066] (1) The pretreated steel plate is subjected to a hot dip plating process in a plating tank, the hot dip plating temperature is 430°C-500°C, the hot dip plating time is 2-10s, and the desired hot dip Zn-Al-Mg alloy plate is obtained after post-treatment.

[0067] (2) The hot-dip Zn-Al-Mg alloy plate is cut by electric spark cutting into a length of 15-16 cm, a width of 10-11 cm, and a thickness of 0.8-0.9 mm.

[0068] (3) The cut plate section is polished and cleaned, ultrasonically treated in anhydrous ethanol for 600 seconds, and acetone is evenly dipped into an ultra-fine dust-free cloth and wiped on the coating surface for 1-2 minutes to further remove any organic pollutants that may exist on the coating surface. The plate is then rinsed with deionized water and dried in an oven at 50°C for 20 minutes to ensure that the surface moisture is completely evaporated.

[0069] (4) High temperature and high humidity treatment: The parameters of the wet heat test chamber used are as follows: humidity range is 20% RH-100% RH, temperature range is -20℃-150℃, effective volume ≥40L, effective box inner dimensions are 350mm in diameter and 50mm in depth, temperature fluctuation is ±0.3℃, temperature uniformity is 3.0℃, temperature deviation is ±3.0℃, absolute pressure range is 100-300Kpa, and pressure deviation is ±2Kpa.

[0070] (5) The experimental temperature was set to 130°C, the humidity was set to 90% RH, and the treatment time was set to 3 h, and the samples were subjected to high temperature and high humidity treatment.

[0071] Example 7

[0072] A method for blackening the surface of a hot-dip Zn-Al-Mg alloy coating, wherein the hot-dip Zn-Al-Mg alloy coating comprises the following components by mass percentage: Al 5.0-15.0wt.%, Mg 2.0-4.0wt.%, Si 0.1-0.3wt.%, and the balance is Zn, and the blackening method comprises the following steps:

[0073] (1) The pretreated steel plate is subjected to a hot dip plating process in a plating tank, the hot dip plating temperature is 430°C-500°C, the hot dip plating time is 2-10s, and the desired hot dip Zn-Al-Mg alloy plate is obtained after post-treatment.

[0074] (2) The hot-dip Zn-Al-Mg alloy plate is cut by electric spark cutting into a length of 15-16 cm, a width of 10-11 cm, and a thickness of 0.8-0.9 mm.

[0075] (3) The cut plate section is polished and cleaned, ultrasonically treated in anhydrous ethanol for 600 seconds, and acetone is evenly dipped into an ultra-fine dust-free cloth and wiped on the coating surface for 1-2 minutes to further remove any organic pollutants that may exist on the coating surface. The plate is then rinsed with deionized water and dried in an oven at 50°C for 20 minutes to ensure that the surface moisture is completely evaporated.

[0076] (4) High temperature and high humidity treatment: The parameters of the wet heat test chamber used are as follows: humidity range is 20% RH-100% RH, temperature range is -20℃-150℃, effective volume ≥40L, effective box inner dimensions are 350mm in diameter and 50mm in depth, temperature fluctuation is ±0.3℃, temperature uniformity is 3.0℃, temperature deviation is ±3.0℃, absolute pressure range is 100-300Kpa, and pressure deviation is ±2Kpa.

[0077] (5) Set the experimental temperature to 130°C, the humidity to 100% RH, and the treatment time to 3 h to subject the sample to high temperature and high humidity treatment.

[0078] Example 8

[0079] A method for blackening the surface of a hot-dip Zn-Al-Mg alloy coating, wherein the hot-dip Zn-Al-Mg alloy coating comprises the following components by mass percentage: Al 5.0-15.0wt.%, Mg 2.0-4.0wt.%, Si 0.1-0.3wt.%, and the balance is Zn, and the blackening method comprises the following steps:

[0080] (1) The pretreated steel plate is subjected to a hot dip plating process in a plating tank, the hot dip plating temperature is 430°C-500°C, the hot dip plating time is 2-10s, and the desired hot dip Zn-Al-Mg alloy plate is obtained after post-treatment.

[0081] (2) The hot-dip Zn-Al-Mg alloy plate is cut by electric spark cutting into a length of 15-16 cm, a width of 10-11 cm, and a thickness of 0.8-0.9 mm.

[0082] (3) The cut plate section is polished and cleaned, ultrasonically treated in anhydrous ethanol for 600 seconds, and acetone is evenly dipped into an ultra-fine dust-free cloth and wiped on the coating surface for 1-2 minutes to further remove any organic pollutants that may exist on the coating surface. The plate is then rinsed with deionized water and dried in an oven at 50°C for 20 minutes to ensure that the surface moisture is completely evaporated.

[0083] (4) High temperature and high humidity treatment: The parameters of the wet heat test chamber used are as follows: humidity range is 20% RH-100% RH, temperature range is -20℃-150℃, effective volume ≥40L, effective box inner dimensions are 350mm in diameter and 50mm in depth, temperature fluctuation is ±0.3℃, temperature uniformity is 3.0℃, temperature deviation is ±3.0℃, absolute pressure range is 100-300Kpa, and pressure deviation is ±2Kpa.

[0084] (5) The experimental temperature was set to 130°C, the humidity was set to 100% RH, and the treatment time was set to 4.5 h, and the samples were subjected to high temperature and high humidity treatment.

[0085] Example 9

[0086] A method for blackening the surface of a hot-dip Zn-Al-Mg alloy coating, wherein the hot-dip Zn-Al-Mg alloy coating comprises the following components by mass percentage: Al 5.0-15.0wt.%, Mg 2.0-4.0wt.%, Si 0.1-0.3wt.%, and the balance is Zn, and the blackening method comprises the following steps:

[0087] (1) The pretreated steel plate is subjected to a hot dip plating process in a plating tank, the hot dip plating temperature is 430°C-500°C, the hot dip plating time is 2-10s, and the desired hot dip Zn-Al-Mg alloy plate is obtained after post-treatment.

[0088] (2) The hot-dip Zn-Al-Mg alloy plate is cut by electric spark cutting into a length of 15-16 cm, a width of 10-11 cm, and a thickness of 0.8-0.9 mm.

[0089] (3) The cut plate section is polished and cleaned, ultrasonically treated in anhydrous ethanol for 600 seconds, and acetone is evenly dipped into an ultra-fine dust-free cloth and wiped on the coating surface for 1-2 minutes to further remove any organic pollutants that may exist on the coating surface. The plate is then rinsed with deionized water and dried in an oven at 50°C for 20 minutes to ensure that the surface moisture is completely evaporated.

[0090] (4) High temperature and high humidity treatment: The parameters of the wet heat test chamber used are as follows: humidity range is 20% RH-100% RH, temperature range is -20℃-150℃, effective volume ≥40L, effective box inner dimensions are 350mm in diameter and 50mm in depth, temperature fluctuation is ±0.3℃, temperature uniformity is 3.0℃, temperature deviation is ±3.0℃, absolute pressure range is 100-300Kpa, and pressure deviation is ±2Kpa.

[0091] (5) The experimental temperature was set to 130°C, the humidity was set to 100% RH, and the treatment time was set to 6 h, and the samples were subjected to high temperature and high humidity treatment.

[0092] It should be noted that, in this article, relational terms such as first and second, etc. 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. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0093] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A hot-dip Zn-Al-Mg alloy coating, characterized in that: The composition includes the following components by mass percentage: Al 5.0-15.0wt.%, Mg 2.0-4.0wt.%, Si 0.1-0.3wt.%, and the balance is Zn.

2. A hot-dip Zn-Al-Mg alloy coating blackening method according to claim 1, characterized in that: The steps include: (1) hot-dip plating is performed on the pre-treated steel sheet in a plating tank, and then a series of post-treatments are performed to obtain a Zn-Al-Mg alloy plate; (2) cutting the hot-dip Zn-Al-Mg alloy plate into specified sizes by electric spark cutting; (3) ultrasonically clean the cut plates, rinse and dry them; (4) placing the plate obtained in step (3) into a wet heat test chamber; (5) The wet heat test chamber is set to a predetermined temperature, humidity and time, and a hot-dip Zn-Al-Mg alloy plate with a blackened surface can be obtained.

3. A method for blackening a hot-dip Zn-Al-Mg alloy coating according to claim 2, characterized in that: The hot-dip coating temperature in step (1) is 430° C.-500° C., the hot-dip coating time is 2-10 s, and the thickness of the alloy coating is 10-60 μm.

4. A method for blackening a hot-dip Zn-Al-Mg alloy coating according to claim 3, characterized in that: The dimensions of the product after the electric spark cutting in step (2) are 15-16 cm in length, 10-11 cm in width and 0.8-0.9 mm in thickness.

5. A method for blackening a hot-dip Zn-Al-Mg alloy coating according to claim 4, characterized in that: In the step (3), the plate is ultrasonically treated in anhydrous ethanol, and after the ultrasonic treatment is completed, it is wiped with acetone and anhydrous ethanol, washed with deionized water and dried for later use.

6. A method for blackening a hot-dip Zn-Al-Mg alloy coating according to claim 5, characterized in that: In the step (3), the ultrasonic time of anhydrous ethanol is 600 s. Acetone is evenly dipped into an ultra-fine dust-free cloth and wiped on the surface of the coating for 12 minutes. The coating is then rinsed with deionized water and dried in an oven at 50° C. for 20 minutes.

7. A method for blackening a hot-dip Zn-Al-Mg alloy coating according to claim 6, characterized in that: The humidity range of the heat and humidity test chamber used in step (4) is 20% RH-100% RH, the temperature range is -20°C-150°C, the effective volume is ≥40L, the effective box inner dimensions are 350mm in diameter, 50mm in depth, the temperature fluctuation is ±0.3°C, the temperature uniformity is 3.0°C, the temperature deviation is ±3.0°C, the absolute pressure range is 100-300Kpa, and the pressure deviation is ±2Kpa.

8. A method for blackening a hot-dip Zn-Al-Mg alloy coating according to claim 7, characterized in that: The experimental temperature in step (5) is 80° C.-140° C., the experimental humidity is 60% RH-100% RH, the experimental time is 3h-10h, and the water source used for humidification is drinking purified water.

Images