Why do we need zinc dipping before electroless nickel plating on aluminum alloy? The main purpose of this is to improve the bonding force of the nickel layer on the surface of the aluminum alloy. The naturally formed oxide layer on the surface of aluminum alloy and its unique chemical characteristics will lead to weak adhesion during direct electroless plating or electroplating, and the aluminum surface is not easy to directly catalyze, which is not conducive to the cohesiveness and uniformity of the coating.
Zinc dipping treatment is to form a thin layer of zinc on the surface of aluminum alloy through a chemical displacement reaction before electroless plating or electroplating. This layer of zinc can be used as a sacrificial cathode layer and has several functions:
1. Improve the binding force: the combination of zinc layer and nickel plating layer is much stronger than the combination of aluminum and nickel directly.
2. Catalytic surface: Because zinc is easier to catalyze than aluminum, this thin layer of zinc can act as a "catalytic bed" to help trigger the subsequent chemical deposition of the nickel coating.
3. Prevent oxidation: The zinc layer can temporarily prevent the surface of the aluminum alloy from being oxidized again, and keep the surface of the aluminum as clean and active as possible in the next nickel plating treatment.
4. Reduce defects: The smooth and continuous zinc layer formed on the surface of the aluminum alloy can reduce the holes in the subsequent nickel layer.
Therefore, the binding force and overall quality of the electroless nickel plating layer on the surface of aluminum alloy can be improved by using Bigely BC-22 zinc precipitating water for treatment. This treatment is a common step in the surface treatment of aluminum alloys and is especially suitable for applications where coating properties have special requirements.
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