A method for preparing Ni / P coating on the surface of Al-Mg-Si alloy plate

Abstract

This invention relates to the field of Al-Mg-Si alloy plates, specifically to a method for preparing a Ni / P coating on the surface of an Al-Mg-Si alloy plate. The invention first generates a hydrophilic surface film on the Al-Mg-Si alloy surface, then deposits a strong and uniform zinc layer using the hydrophilic film in a zinc immersion process, followed by nickel plating in an alkaline solution, and then Ni / P plating in an acidic solution. Finally, a heat treatment process is used to eliminate the hydrophilic film on the surface and reduce defects in the coating. The advantages of this invention are: (1) the presence of a good hydrophilic surface film accelerates the deposition of the zinc plating layer and the Ni / P plating layer on the alloy surface; (2) heat treatment in a vacuum environment eliminates the hydrophilic film on the surface and reduces defects in the coating, resulting in a smooth, bright, dense, uniform, strong, and corrosion-resistant Ni / P coating; (3) the method of this invention is simple, energy-efficient, and low-cost, possessing great practical and promotional value.

Description

Technical Field

[0001] The invention relates to the field of Al-Mg-Si alloy pole plates, and in particular to a method for preparing a Ni / P coating on the surface of an Al-Mg-Si alloy pole plate. Background Art

[0002] In the 21st century, traditional steel materials can no longer fully meet human requirements, so lightweight materials such as aluminum alloys have emerged. Aluminum and aluminum alloys are the most widely used lightweight metal materials among non-ferrous metals. They have many excellent physical, chemical, mechanical and processing properties and characteristics, such as low density, corrosion resistance, good conductivity, easy strengthening, and easy surface treatment. However, as the manufacturing industry has increasingly higher requirements for the use of materials, people have higher standards for the performance of materials. In recent years or even decades, aluminum and aluminum alloys have been widely used in industries such as aviation, aerospace, automobiles, electronics, and household appliances after being treated with various surface treatment technologies.

[0003] Chemical plating of Ni / P alloy on the surface of aluminum-based materials is currently a good surface treatment process. The resulting coating has the advantages of corrosion resistance, high surface hardness, wear resistance, and decorative properties, which can extend the service life of the aluminum base and expand its application range. However, aluminum and its alloys are difficult to plate metals for the following reasons: 1) They have a high affinity for oxygen and are prone to form an oxide film on the surface when in contact with air, which seriously affects the bonding strength of the coating; 2) They have a low standard potential and strong electronegativity, which makes it easy for them to quickly undergo a replacement reaction with metal (nickel) ions with a higher positive potential in the plating solution; 3) Due to the occurrence of the replacement reaction, aluminum ions will become impurity ions and enter the plating solution, affecting the stability of the plating solution.

[0004] In the publication number CN111364030A, entitled "A pretreatment method for improving the flatness of chemically plated NiP coating on aluminum substrate", the surface of the aluminum substrate is first pretreated by degreasing and pickling processes, and then immersed in a Cu-containing 2+ In an acidic solution, a thin copper film is first prepared on the surface of the aluminum to make it an active point during zinc immersion. Then, a secondary zinc immersion is performed to prepare a fine and uniform zinc layer on the surface of the substrate, thereby obtaining a Ni / P coating with significantly improved flatness after chemical plating. Although the process is simple and the cost is low, it is difficult to immerse aluminum in a Cu-containing solution. 2+In an acidic solution, an uneven Al-Cu phase may be generated on the aluminum and surface, which will become the cathode phase of galvanic corrosion in the acidic solution, forming more corrosion pits on the alloy surface, which may eventually cause the coating surface to be uneven. In the publication number CN108034932A, entitled "A process for chemical nickel-phosphorus plating on the surface of 7A19 aluminum alloy material", a secondary zinc immersion method is used to chemically plate Ni / P on the surface of 7A19 aluminum alloy. The prepared Ni / P coating has good bonding with the substrate, and the coating not only has high brightness, but also has dense and uniform crystals. However, under the conditions of 86-88°C and PH of 4.4-4.6, the alloy needs to be plated in the chemical nickel-phosphorus plating solution for 2-5 hours, and the secondary zinc plating process is more cumbersome than the primary zinc plating process. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing Ni / P coating on the surface of Al-Mg-Si alloy plate, combining the presence of a surface film with good hydrophilicity to accelerate the deposition of Ni / P coating on the alloy surface, and finally removing the hydrophilic film and reducing the defects in the coating by heat treatment in a vacuum environment. The method has the advantages of simple process, low cost, mild reaction conditions, etc., and has great practical and promotion value.

[0006] The technical solution adopted by the present invention is:

[0007] A method for preparing a Ni / P coating on the surface of an Al-Mg-Si alloy plate comprises the following steps:

[0008] (8) Material preparation: The Al-Mg-Si alloy plate has the following element weight percentages: Mg element accounts for 0.8-1.2 wt.%, Si element accounts for 0.4-0.8 wt.%, and the remainder is Al and unavoidable impurities.

[0009] (9) Degreasing and removing impurities from the electrode plates: The electrode plates were polished with 400#, 1000#, 2000#, and 5000# sandpapers in sequence, and then the aluminum alloy plates were ultrasonically cleaned in ethanol and acetone for 5 to 10 minutes in sequence, and ultrasonically cleaned with deionized water for 5 to 10 minutes. Finally, they were corroded with 10% NaOH solution at a temperature of 50 to 70°C for 1 to 2 minutes to remove the surface oxide film, and placed in a vacuum drying oven for later use.

[0010] (10) Solution preparation: 1) Hydrophilic membrane mixed solution: 1.0-1.5 g / L polyvinyl alcohol, 0.15-0.25 g / L glyoxal, and the rest is deionized water. 2) Zinc immersion solution: 100-150 g / L NaOH, 8-12 g / L ZnO, 8-12 g / L NiCl2, 1-1.5 g / L FeCl3, 1-1.2 g / L NaNO2, appropriate amount of complexing agent, and the rest is deionized water. 3) Alkaline nickel immersion solution: 20-30g / L nickel sulfate, 20-30g / L sodium hypophosphite, 40-60g / L ammonium citrate, adjust the pH value to 9-11. 4) Acidic Ni / P plating solution: 250-300g / L nickel sulfate, 30-40g / L nickel chloride, 300-400g / L sodium hypophosphite, 40-50g / L citric acid, 1.5-2.5g / L benzenesulfonic acid main brightener content, appropriate amount of organic phosphate complexing agent, and the rest is deionized water, adjust the pH to 4.5-5.

[0011] (11) Surface zinc immersion: Soak the degreased and impurity-free plates in a hydrophilic film solution for 30 to 60 seconds to form a thin hydrophilic film on the surface of the plates. Place the plates with the hydrophilic film in a zinc immersion solution for 60 to 90 seconds to deposit a uniform and fine zinc layer on the surface, then rinse the surface with deionized water at 75 to 85°C, and then rinse with cold deionized water.

[0012] (12) Alkaline nickel immersion: Place the zinc-immersed plate in an alkaline nickel immersion solution for 3 to 5 minutes, maintaining the temperature at 30 to 50°C, then rinse the surface with deionized water at 75 to 85°C, and then rinse with cold deionized water.

[0013] (13) Chemical nickel plating: Immerse the nickel-plated electrode in a hydrophilic film solution for 30 to 60 minutes to form a thin hydrophilic film on the surface of the electrode. Then, chemical nickel plating is performed on the electrode in an acidic Ni / P plating solution for 60 to 90 minutes, and the temperature is maintained at 75 to 85°C.

[0014] (14) Heat treatment: Finally, the plate is annealed in vacuum at 300-350°C for 120-180 min to remove the hydrophilic film and reduce defects in the coating to obtain an Al-Mg-Si alloy plate with a uniform bright Ni / P coating.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention first generates a hydrophilic surface film on the surface of the Al-Mg-Si alloy, deposits a firm and uniform zinc layer through the hydrophilic film in a zinc immersion method, then nickel is plated in an alkaline solution, and then a Ni / P layer is plated in an acidic solution, and finally a heat treatment process is used to eliminate the hydrophilic film on the surface and reduce defects in the coating. The present invention has the following unique features: (1) the presence of a good hydrophilic surface film is combined to accelerate the deposition of the zinc plating layer and the Ni / P plating layer on the alloy surface; (2) the hydrophilic film on the surface is eliminated and the defects in the coating are reduced by heat treatment in a vacuum environment, so as to obtain a flat, bright, dense, uniform, firm and corrosion-resistant Ni / P coating; (3) the method of the present invention is simple in process, low in energy consumption, low in cost, and has great practical and promotion value. DETAILED DESCRIPTION

[0017] The present invention will be further illustrated by the following examples.

[0018] Example 1.

[0019] (1) Material preparation: The Al-Mg-Si alloy plate has the following element weight percentages: Mg element accounts for 0.8wt.%, Si element accounts for 0.6wt.%, and the remainder is Al and unavoidable impurities.

[0020] (2) Degreasing and removing impurities from the electrode plates: The electrode plates were polished with 400#, 1000#, 2000#, and 5000# sandpapers in sequence, and then the aluminum alloy plates were ultrasonically cleaned in ethanol and acetone for 10 min in sequence, and ultrasonically cleaned with deionized water for 5 min. Finally, they were corroded with 10% NaOH solution at 60°C for 2 min to remove the surface oxide film, and placed in a vacuum drying oven for later use.

[0021] (3) Solution preparation: 1) Hydrophilic membrane mixed solution: 1.5 g / L polyvinyl alcohol, 0.25 g / L glyoxal, and the rest is deionized water. 2) Zinc immersion solution: 140 g / L NaOH, 12 g / L ZnO, 10 g / L NiCl2, 1.3 g / L FeCl3, 1.1 g / L NaNO2, appropriate amount of complexing agent, and the rest is deionized water. 3) Alkaline nickel immersion solution: 30g / L nickel sulfate, 30g / L sodium hypophosphite, 60g / L ammonium citrate, adjust the pH to 11. 4) Acidic Ni / P plating solution: 300g / L nickel sulfate, 40g / L nickel chloride, 400g / L sodium hypophosphite, 50g / L citric acid, 1.5g / L benzenesulfonic acid main brightener, appropriate amount of organic phosphate complexing agent, and the rest is deionized water, adjust the pH to 4.8.

[0022] (4) Surface zinc immersion: Soak the degreased and impurity-free plates in a hydrophilic film solution for 40 seconds to form a thin hydrophilic film on the surface of the plates. Place the plates with the hydrophilic film in a zinc immersion solution for 75 seconds to deposit a uniform and fine zinc layer on the surface, then rinse the surface with 85°C deionized water and then rinse with cold deionized water.

[0023] (5) Alkaline nickel immersion: Place the zinc-immersed plate in an alkaline nickel immersion solution for 3 minutes, keep the temperature at 40°C, then rinse the surface with 75°C deionized water, and then rinse with cold deionized water.

[0024] (6) Chemical nickel plating: The plate after nickel immersion is immersed in a hydrophilic film solution for 40 minutes to form a thin hydrophilic film on the surface of the plate. The plate is then chemically nickel plated in an acidic Ni / P plating solution for 80 minutes at a temperature of 75°C.

[0025] (7) Heat treatment: Finally, the plate was annealed at 320 °C for 160 min in vacuum to remove the hydrophilic film and reduce defects in the coating to obtain an Al-Mg-Si alloy plate with a uniform bright Ni / P coating.

[0026] Under the above conditions, the prepared coating is smooth, bright, dense and uniform, the coating does not peel off, and the substrate is not corroded after being immersed in 10% NaOH solution for 10 hours.

[0027] Example 2.

[0028] (1) Material preparation: The Al-Mg-Si alloy plate has the following element weight percentages: Mg element accounts for 1.0wt.%, Si element accounts for 0.6wt.%, and the remainder is Al and unavoidable impurities.

[0029] (2) Degreasing and removing impurities from the electrode plates: The electrode plates were polished with 400#, 1000#, 2000#, and 5000# sandpapers in sequence, and then the aluminum alloy plates were ultrasonically cleaned in ethanol and acetone for 8 minutes in sequence, and ultrasonically cleaned with deionized water for 6 minutes. Finally, they were corroded with 10% NaOH solution at 65°C for 1 minute to remove the surface oxide film, and placed in a vacuum drying oven for later use.

[0030] (3) Solution preparation: 1) Hydrophilic membrane mixed solution: 1.2 g / L polyvinyl alcohol, 0.2 g / L glyoxal, and the rest is deionized water. 2) Zinc immersion solution: 110 g / L NaOH, 12 g / L ZnO, 10 g / L NiCl2, 1.4 g / L FeCl3, 1.0 g / L NaNO2, appropriate amount of complexing agent, and the rest is deionized water. 3) Alkaline nickel immersion solution: 24g / L nickel sulfate, 23g / L sodium hypophosphite, 45g / L ammonium citrate, adjust the pH to 10. 4) Acidic Ni / P plating solution: 270g / L nickel sulfate, 35g / L nickel chloride, 320g / L sodium hypophosphite, 50g / L citric acid, 2.0g / L benzenesulfonic acid main brightener, appropriate amount of organic phosphate complexing agent, and the rest is deionized water, adjust the pH to 4.6.

[0031] (4) Surface zinc immersion: Soak the degreased and impurity-free plates in a hydrophilic film solution for 45 seconds to form a thin hydrophilic film on the surface of the plates. Place the plates with the hydrophilic film in a zinc immersion solution for 80 seconds to deposit a uniform and fine zinc layer on the surface, then rinse the surface with 80°C deionized water and then rinse with cold deionized water.

[0032] (5) Alkaline nickel immersion: Place the zinc-immersed plate in an alkaline nickel immersion solution for 4 minutes, keep the temperature at 40°C, then rinse the surface with 80°C deionized water, and then rinse with cold deionized water.

[0033] (6) Chemical nickel plating: The plate after nickel immersion is immersed in a hydrophilic film solution for 45 minutes to form a thin hydrophilic film on the surface of the plate. The plate is then chemically nickel plated in an acidic Ni / P plating solution for 80 minutes at a temperature of 85°C.

[0034] (7) Heat treatment: Finally, the plate was annealed at 350 °C for 120 min in vacuum to remove the hydrophilic film and reduce defects in the coating to obtain an Al-Mg-Si alloy plate with a uniform bright Ni / P coating.

[0035] Under the above conditions, the prepared coating is smooth, bright, dense and uniform, the coating does not peel off, and the substrate is not corroded after being immersed in 10% NaOH solution for 10 hours.

[0036] Example 3.

[0037] (1) Material preparation: The Al-Mg-Si alloy plate has the following element weight percentages: Mg element accounts for 1.2wt.%, Si element accounts for 0.8wt.%, and the remainder is Al and unavoidable impurities.

[0038] (2) Degreasing and removing impurities from the electrode plates: The electrode plates were polished with 400#, 1000#, 2000#, and 5000# sandpapers in sequence, and then the aluminum alloy plates were ultrasonically cleaned in ethanol and acetone for 6 minutes in sequence, and ultrasonically cleaned with deionized water for 8 minutes. Finally, they were corroded with 10% NaOH solution at 65°C for 1.5 minutes to remove the surface oxide film, and placed in a vacuum drying oven for later use.

[0039] (3) Solution preparation: 1) Hydrophilic membrane mixed solution: 1.0 g / L polyvinyl alcohol, 0.15 / L glyoxal, and the rest is deionized water. 2) Zinc immersion solution: 120 g / L NaOH, 10 g / L ZnO, 9 g / L NiCl2, 1.2 g / L FeCl3, 1.2 g / L NaNO2, appropriate amount of complexing agent, and the rest is deionized water. 3) Alkaline nickel immersion solution: 25g / L nickel sulfate, 26g / L sodium hypophosphite, 52g / L ammonium citrate, adjust the pH to 11. 4) Acidic Ni / P plating solution: 280g / L nickel sulfate, 35g / L nickel chloride, 330g / L sodium hypophosphite, 45g / L citric acid, 1.8g / L benzenesulfonic acid main brightener, appropriate amount of organic phosphate complexing agent, and the rest is deionized water, adjust the pH to 4.9.

[0040] (4) Surface zinc immersion: Soak the degreased and impurity-free plates in a hydrophilic film solution for 50 seconds to form a thin hydrophilic film on the surface of the plates. Place the plates with the hydrophilic film in a zinc immersion solution for 90 seconds to deposit a uniform and fine zinc layer on the surface, then rinse the surface with 75°C deionized water and then rinse with cold deionized water.

[0041] (5) Alkaline nickel immersion: Place the zinc-immersed plate in an alkaline nickel immersion solution for 5 minutes, keep the temperature at 30-50°C, then rinse the surface with 75°C deionized water, and then rinse with cold deionized water.

[0042] (6) Chemical nickel plating: Immerse the nickel-plated electrode in a hydrophilic film solution for 30 minutes to form a thin hydrophilic film on the surface of the electrode. Then, chemical nickel plating is performed on the electrode in an acidic Ni / P plating solution for 90 minutes at a temperature of 80°C.

[0043] (7) Heat treatment: Finally, the plate was annealed at 300 °C for 180 min in vacuum to remove the hydrophilic film and reduce defects in the coating to obtain an Al-Mg-Si alloy plate with a uniform bright Ni / P coating.

[0044] Under the above conditions, the prepared coating is smooth, bright, dense and uniform, the coating does not peel off, and the substrate is not corroded after being immersed in 10% NaOH solution for 10 hours.

[0045] The above only expresses the preferred embodiments of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications, improvements and substitutions can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A method for preparing a Ni / P coating on the surface of an Al-Mg-Si alloy plate, characterized in that: The specific steps include: (1) Material preparation: The Al-Mg-Si alloy plate has the following element weight percentages: Mg element accounts for 0.8-1.2wt.%, Si element accounts for 0.4-0.8wt.%, and the balance is Al and unavoidable impurities; (2) Degreasing and removing impurities from the electrode plates: The electrode plates were polished with 400#, 1000#, 2000#, and 5000# sandpapers in sequence, and then the aluminum alloy plates were ultrasonically cleaned in ethanol and acetone for 5 to 10 minutes in sequence, and ultrasonically cleaned with deionized water for 5 to 10 minutes, and finally, they were corroded with 10% NaOH solution at a temperature of 50 to 70°C for 1 to 2 minutes to remove the surface oxide film, and then placed in a vacuum drying oven for use; (3) Solution preparation: 1) Hydrophilic membrane mixed solution: 1.0-1.5 g / L polyvinyl alcohol, 0.15-0.25 g / L glyoxal, and the rest is deionized water; 2) Zinc immersion solution: 100-150 g / L NaOH, 8-12 g / L ZnO, 8-12 g / L NiCl2, 1-1.5 g / L% FeCl3, 1-1.2 g / L NaNO2, appropriate amount of complexing agent, and the rest is deionized water; 3) Alkaline nickel immersion solution: 20-30 g / L nickel sulfate, 20-30g / L sodium hypophosphite, 40-60g / L ammonium citrate, adjust the pH value to 9-11; 4) acidic Ni / P plating solution: 250-300g / L nickel sulfate, 30-40g / L nickel chloride, 300-400g / L sodium hypophosphite, 40-50g / L citric acid, 1.5-2.5g / L benzenesulfonic acid main brightener content, appropriate amount of organic phosphate complexing agent, the rest is deionized water, adjust the pH to 4.5-5; (4) Surface zinc immersion: Soak the degreased and impurity-free electrode plate in a hydrophilic film solution for 30 to 60 seconds to form a hydrophilic film on the surface of the electrode plate; place the electrode plate with the hydrophilic film in the zinc immersion solution for 60 to 90 seconds to deposit a uniform and fine zinc layer on its surface, then rinse the surface with deionized water at 75 to 85°C, and then rinse with cold deionized water; (5) Alkaline nickel immersion: Place the zinc-immersed plate in an alkaline nickel immersion solution for 3 to 5 minutes, keep the temperature at 30 to 50°C, then rinse the surface with deionized water at 75 to 85°C, and then rinse with cold deionized water; (6) Chemical nickel plating: Immerse the plate after nickel immersion in a hydrophilic film solution for 30 to 60 minutes to form a thin hydrophilic film on the surface of the plate, and then chemically plate the plate with nickel in an acidic Ni / P plating solution for 60 to 90 minutes, with the temperature maintained at 75 to 85°C; (7) Heat treatment: Finally, the plate is annealed in vacuum at 300-350°C for 120-180 min to remove the hydrophilic film and reduce defects in the coating to obtain an Al-Mg-Si alloy plate with a uniform bright Ni / P coating.