Black zinc-aluminum-magnesium coated steel plate and preparation method thereof

Abstract

The invention discloses a black zinc-aluminum-magnesium coated steel plate and a preparation method thereof, the method comprises two procedures of pretreatment and micro-arc oxidation, micro-arc oxidation in-situ coloring treatment is carried out by adopting a micro-arc oxidation method, the zinc-aluminum-magnesium coated steel plate is an anode, and stainless steel or graphite is a cathode; the preparation method is simple and does not need to be carried out in a high-temperature and high-pressure closed container, and the production process is safer; the production cycle is short, the production efficiency is high and the production cost is low; the prepared black zinc-aluminum coated steel plate is low in lightness L * value and good in blackening uniformity, enriches the appearance tone of the zinc-aluminum-magnesium coated steel plate, is good in decorative effect, can meet the requirements of the steel plate with black appearance, and has wide application prospects in the fields of photovoltaics, household appliances, automobiles, buildings and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-dip galvanized aluminum-magnesium steel plates, and specifically relates to a black zinc-aluminum-magnesium coated steel plate and a preparation method thereof. Background Art

[0002] Zinc-aluminum-magnesium coated steel sheet is a new type of environmentally friendly and energy-saving steel sheet that is suitable for various harsh environments due to its corrosion resistance, wear resistance, coating resistance and good welding processing performance. It is widely used in photovoltaic, automobile, home appliance and equipment manufacturing and other fields. The surface of zinc-aluminum-magnesium coating has good metallic luster and is silvery white. In recent years, with the growing demand for coated steel sheets with black appearance in the fields of building roof materials, outer packaging materials, home appliances, automobiles, etc. In order to obtain a black appearance with higher design, a black paint coating method is currently used. In order to hide the base color of the coated steel sheet, the coating thickness must be increased, resulting in a series of problems such as high coating cost, poor adhesion between the coating and the plating, and easy shedding.

[0003] The prior art method for preparing black coatings no longer needs to use black paint to cover the silvery-white metallic luster of the coated steel plate. Black oxides can be formed by reacting high-temperature water vapor with the surface of the coated steel plate, and the distribution of water vapor and the content of blackening promoting elements in the coating can be adjusted to prepare a coated steel plate with uniform blackening and low lightness L*. However, the method of preparing a black coated steel plate by reacting high-temperature water vapor with a coated steel plate usually needs to be carried out in a specific or closed container, and the reaction time is long; for example, patent CN201380020982 discloses that it takes about 2 hours to prepare a black coated steel plate under 250°C high-temperature water vapor, which seriously restricts the production efficiency of the black coated steel plate and increases the production cost. In addition, since the method of preparing a black coated steel plate by reacting high-temperature water vapor with the surface of the coated steel plate uses a specific or closed container, it may be restricted by the container, which may impose certain constraints on the shape and size of the produced black coated steel plate. Summary of the invention

[0004] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to quickly prepare a black zinc-aluminum-magnesium coated steel plate by micro-arc oxidation treatment of the zinc-aluminum-magnesium coated steel plate. The preparation scheme is simple, which greatly reduces the production cost, has high production efficiency, and has a good decorative effect. The reaction process does not require a specific container and a high-temperature heating device. The black coated steel plate has a low lightness L* value and good blackening uniformity, which enriches the appearance color tone of the zinc-aluminum-magnesium coated steel plate.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides a method for preparing a black zinc-aluminum-magnesium coated steel plate, the preparation method comprising two steps of pretreatment and micro-arc oxidation:

[0006] a Pretreatment: Use degreasing liquid to remove the oil stains on the zinc-aluminum-magnesium coated steel plate, rinse it with distilled water, and blow it dry. Immerse the zinc-aluminum-magnesium coated steel plate in a hydrochloric acid solution with a mass fraction of 10% to 20% for pickling for 5 to 10 seconds, then rinse it with water after taking it out to improve the surface reaction activity of the zinc-aluminum-magnesium coating.

[0007] b. Micro-arc oxidation: immerse the zinc-aluminum-magnesium coated steel plate obtained in step a into the prepared electrolyte, and perform micro-arc oxidation in-situ coloring treatment on the zinc-aluminum-magnesium coated steel plate, wherein the zinc-aluminum-magnesium coated steel plate is the anode and stainless steel or graphite is the cathode; after the reaction is completed, take out the steel plate, immediately rinse the surface electrolyte with deionized water, and obtain a black zinc-aluminum-magnesium coated steel plate after drying.

[0008] In the above technical solution, further, the electrolyte in step b is composed of a film-forming agent, a pH regulator, a colorant, an auxiliary film-forming agent and a tip discharge inhibitor.

[0009] Furthermore, the film-forming agent is a silicate or a mixture of a silicate and a phosphate, preferably 3-12 g / L of sodium silicate or a mixture of sodium silicate and sodium phosphate.

[0010] Furthermore, the pH adjuster is potassium hydroxide or sodium hydroxide solution, and the pH value is 10-13.

[0011] Furthermore, the colorant is a copper salt or a vanadium salt, preferably 5 to 10 g / L of copper sulfate or ammonium metavanadate.

[0012] Furthermore, the auxiliary film-forming agent is sodium fluoride with a concentration of 1 to 5 g / L;

[0013] Furthermore, the tip discharge inhibitor is glycerol with a concentration of 5 to 15 g / L.

[0014] Furthermore, the micro-arc oxidation in-situ coloring treatment described in step b has an oxidation time of 2 to 6 minutes, a voltage of 250 to 500 V, a duty cycle of 5% to 40%, a frequency of 100 to 300 Hz, and an electrolyte temperature of 20°C to 50°C.

[0015] A black zinc-aluminum-magnesium coated steel plate prepared by the above method, wherein the black zinc-aluminum-magnesium coated steel plate has a lightness L*≤36.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention adopts a micro-arc oxidation method to prepare a black zinc-aluminum coated steel plate. The preparation method is simple, does not need to be carried out in a high-temperature and high-pressure closed container, and the production is safer; the production cycle is short, the production efficiency is high, and the production cost is low; the black zinc-aluminum coated steel plate has a low lightness L* value and good blackening uniformity, enriches the appearance color tone of the zinc-aluminum-magnesium coated steel plate, has a good decorative effect, can meet the demand for steel plates with a black appearance, and has broad application prospects in the fields of photovoltaics, home appliances, automobiles, and construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the macroscopic morphology of the black zinc-aluminum-magnesium coated steel plate obtained in Example 1. DETAILED DESCRIPTION

[0019] The present invention is further described below in conjunction with specific examples, but the present invention is not limited in any way. To avoid redundant description, the raw materials in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0020] A method for preparing a black zinc-aluminum-magnesium coated steel plate includes two steps of pretreatment and micro-arc oxidation:

[0021] a Pretreatment: Use degreasing liquid to remove the oil stains on the zinc-aluminum-magnesium coated steel plate, rinse with distilled water and blow dry; immerse the zinc-aluminum-magnesium coated steel plate in a hydrochloric acid solution with a mass fraction of 10% to 20% for pickling for 5 to 10 seconds, take it out and rinse it with water;

[0022] b. Micro-arc oxidation: immerse the zinc-aluminum-magnesium coated steel plate obtained in step a into the prepared electrolyte, and perform micro-arc oxidation in-situ coloring treatment on the zinc-aluminum-magnesium coated steel plate, wherein the zinc-aluminum-magnesium coated steel plate is the anode and stainless steel or graphite is the cathode; after the reaction is completed, take out the steel plate, immediately rinse the surface electrolyte with deionized water, and obtain a black zinc-aluminum-magnesium coated steel plate after drying.

[0023] The matters not described in the following embodiments are the same as the description of the above specific implementation methods.

[0024] Example 1

[0025] A black zinc-aluminum-magnesium coated steel plate and a preparation method thereof, the specific process flow is as follows:

[0026] The coating composition of zinc-aluminum-magnesium coated steel plate is 11% Al, 3% Mg, 0.2% Si, and the rest is Zn and other unavoidable impurities; the coating weight is about 270g / m 2First, use alkaline degreasing liquid to remove oil stains on the surface of zinc-aluminum-magnesium coated steel plates. The degreasing liquid composition is 15g / L sodium carbonate, 10g / L sodium phosphate, and 10g / L sodium silicate. The degreasing temperature is about 50°C and the degreasing time is about 3 minutes. After degreasing, quickly rinse with distilled water and blow dry. Then the zinc-aluminum-magnesium coated steel plate after degreasing and cleaning is immersed in a hydrochloric acid solution with a mass fraction of 10% for 5s for activation treatment to improve the surface reaction activity of the coating, rinsed with distilled water, blown dry and immersed in an electrolyte of 5g / L sodium silicate, 5g / L ammonium metavanadate, 1g / L sodium fluoride and 5g / L glycerol, pH 10, wherein the zinc-aluminum-magnesium coated steel plate is the anode, stainless steel or graphite is the cathode, and a multifunctional DC pulse micro-arc oxidation power supply is used to perform micro-arc oxidation treatment on the activated zinc-aluminum-magnesium coated steel plate, the oxidation time is 5min, the voltage is 300V, the duty cycle is 20%, the frequency is 300Hz, the electrolyte temperature is 30°C, and after the micro-arc oxidation is completed, the distilled water is taken out and rinsed several times, and then the steel plate is dried with cold air to obtain a black zinc-aluminum-magnesium coated steel plate.

[0027] The lightness L* of the black zinc-aluminum-magnesium coated steel plate obtained in Example 1 was measured by a colorimeter and was about 28. The blackening was uniform and there was no obvious color difference, which could meet the demand for coated steel plates with black appearance in the fields of building roof materials, outer packaging materials, home appliances, automobiles, etc.

[0028] Example 2

[0029] A black zinc-aluminum-magnesium coated steel plate and a preparation method thereof, the specific process flow is as follows:

[0030] The coating composition of zinc-aluminum-magnesium coated steel plate is 6% Al, 3% Mg, and the rest is Zn and other inevitable impurities. The coating weight is about 120g / m 2 ; First, use alkaline degreasing liquid to remove oil stains on the surface of zinc-aluminum-magnesium coated steel plates. The degreasing liquid composition is 15g / L sodium carbonate, 10g / L sodium phosphate, and 10g / L sodium silicate. The degreasing temperature is about 50°C and the degreasing time is about 3 minutes. After degreasing, quickly rinse with distilled water and blow dry. Then the zinc-aluminum-magnesium coated steel plate after degreasing and cleaning is immersed in a hydrochloric acid solution with a mass fraction of 20% for 6s for activation treatment to improve the surface reaction activity of the coating; after rinsing with distilled water and drying, it is immersed in an electrolyte of 10g / L sodium silicate, 10g / L ammonium metavanadate, 3g / L sodium fluoride and 10g / L glycerol with a pH of 13, wherein the zinc-aluminum-magnesium coated steel plate is an anode and stainless steel or graphite is a cathode; a multifunctional DC pulse micro-arc oxidation power supply is used to perform micro-arc oxidation treatment on the activated zinc-aluminum-magnesium coated steel plate, the oxidation time is 2min, the voltage is 400V, the duty cycle is 40%, the frequency is 300Hz, the electrolyte temperature is 50°C, and after the micro-arc oxidation is completed, the distilled water is taken out for multiple rinsing and then dried with cold air; the black zinc-aluminum-magnesium coated steel plate is obtained.

[0031] The lightness L* of the black zinc-aluminum-magnesium coated steel plate obtained in Example 2 was measured by a colorimeter and was found to be about 36. The blackening was uniform and there was no obvious color difference, which met the demand for coated steel plates with a black appearance in the fields of building roof materials, outer packaging materials, home appliances, automobiles, etc.

[0032] For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a black zinc-aluminum-magnesium coated steel plate, characterized in that: The preparation method includes two steps: pretreatment and micro-arc oxidation: a Pretreatment: Use degreasing liquid to remove the oil stains on the zinc-aluminum-magnesium coated steel plate, rinse with distilled water and blow dry; immerse the zinc-aluminum-magnesium coated steel plate in a hydrochloric acid solution with a mass fraction of 10% to 20% for pickling for 5 to 10 seconds, take it out and rinse it with water; b. Micro-arc oxidation: immerse the zinc-aluminum-magnesium coated steel plate obtained in step a into the prepared electrolyte, and perform micro-arc oxidation in-situ coloring treatment on the zinc-aluminum-magnesium coated steel plate, wherein the zinc-aluminum-magnesium coated steel plate is the anode and stainless steel or graphite is the cathode; after the reaction is completed, take out the steel plate, immediately rinse the surface electrolyte with deionized water, and obtain a black zinc-aluminum-magnesium coated steel plate after drying.

2. The preparation method according to claim 1, characterized in that: The electrolyte in step b is composed of a film-forming agent, a pH regulator, a colorant, an auxiliary film-forming agent and a tip discharge inhibitor.

3. The preparation method according to claim 2, characterized in that: The film-forming agent is a silicate or a mixture of a silicate and a phosphate, preferably 3-12 g / L of sodium silicate or a mixture of sodium silicate and sodium phosphate.

4. The preparation method according to claim 3, characterized in that: The pH regulator is potassium hydroxide or sodium hydroxide solution, and the pH value is 10-13.

5. The preparation method according to claim 4, characterized in that: The colorant is a copper salt or a vanadium salt, preferably 5 to 10 g / L of copper sulfate or ammonium metavanadate.

6. The preparation method according to claim 5, characterized in that: The auxiliary film-forming agent is sodium fluoride with a concentration of 1 to 5 g / L; the tip discharge inhibitor is glycerol with a concentration of 5 to 15 g / L.

7. The preparation method according to claim 6, characterized in that: The micro-arc oxidation in-situ coloring treatment described in step b has an oxidation time of 2 to 6 minutes, a voltage of 250 to 500 V, a duty cycle of 5% to 40%, a frequency of 100 to 300 Hz, and an electrolyte temperature of 20°C to 50°C.

8. A black zinc-aluminum-magnesium coated steel sheet prepared according to any one of claims 1 to 7, characterized in that: The black zinc-aluminum-magnesium coated steel plate has a lightness L*≤36.

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