ã€China Aluminum Industry Network】Micro aluminum parts (amplifier aluminum cavity, microwave switches, oscillators and antenna eclipses, etc.) Electroless nickel plating instead of aluminum silver plating process must ensure the appearance of decorative, excellent adhesion, corrosion resistance and Ideal physical and chemical properties (electromagnetic shielding, weldability, high hardness, wear resistance, high and low temperature, etc.). The key is to optimize the process recipe and coating combination.
Typical process flow: organic solvent support (LYC2 is aluminized) → alkaline degreasing (alkali corrosion) → nitric acid etching → secondary zincation → alkaline electroless nickel plating → acidic electroless nickel plating → heat treatment (1) The improved special pretreatment process selected modified zincate with nickel salt and an auxiliary complexing agent. The alkali concentration was moderate, especially nickel salt. The content of potassium sodium tartrate was increased, and additives were added to increase the nickel ion content. The more stable ion-opening exists, so that the nickel ions and the zinc ions are slowly and uniformly displaced and deposited on the aluminum surface, and the obtained zinc-nickel alloy layer is thinner and more uniform than the zinc-impregnated layer obtained from the conventional zinc-immersion solution. The control of the weight of Zn-Ni layer in the range of 1 to 2 mg/dm2 can fully ensure good adhesion and corrosion resistance of the coating on the aluminum; in particular, the nickel-containing zinc layer provides a sufficient catalytic core for the subsequent initial deposition of electroless nickel plating. A uniform fine nucleus is obtained, which is an important factor for improving the adhesion of the subsequent nickel plating layer.
(2) Improvement of the pre-plated underlayer Since the zinc layer is resistant to liquid corrosion, it must be pre-plated with alkaline electroless nickel as the underlayer. However, the alkaline nickel plating solution has the disadvantages of slow deposition rate (5~10m), low P content (4%~6%), and poor corrosion resistance. It is required to change the concentration of retreating agent and complexing agent, select the PH value range during the better period, ensure the stability of plating solution, and the plating speed is moderate, and can obtain a layer of pre-plated thin nickel layer with fine crystals and uniform bonding with the substrate on the surface of the zincation layer. .
(3) Improving the protection and decoration of the coating The preferred acidic electroless nickel plating formula contains a small amount of brightener, and the molar ratio of nickel ion to hypophosphite is controlled at about 0.4 to ensure a moderate plating rate (16 to 20 m/h). ), The solution is stable (more than 6 cycles, even if the bath is not dissolved). In addition, complex complexing agents are added to prevent precipitation of nickel phosphite. The bright yellow-white nickel layer (phosphorus content 8%~10%) can be plated from this liquid and has good corrosion resistance (25 μm nickel layer thickness, neutral salt spray test 48 h, corrosion resistance grade 9.5). It is recommended that the thickness of electroless nickel plating for workpieces used in harsh environments is designed to be ≥25 μm.
(4) Appropriate post-treatment aluminum alloy electroless nickel plating heat treatment (150 ~ 200oC, 3h), can eliminate residual H atoms in the layer, relax the internal stress, and further increase the adhesion and hardness of the coating and the substrate.
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