Notes on silver plating of aluminium machined parts.

The silver plating of aluminum machined parts is much more difficult than that of ordinary copper parts, and the process is complicated. The main reason is that the performance of aluminum machined parts is different from that of other metals. Aluminum belongs to amphoteric metal and reacts with acid and base. If the pretreatment is a little improper, it will lead to surface corrosion. Moreover, aluminum machined parts are easy to produce oxide film in air or in solution. If the oxide film is not removed, it will affect the bonding strength of the coating.

The key to silver plating of aluminum machined parts is the adhesion between the coating and the base metal. Therefore, a special treatment must be adopted to obtain a silver coating with good bonding strength on the aluminum substrate. The method of dipping zinc can solve the difficult problem.

The principle of dipping zinc is to replace the thin layer of zinc by using the principle that aluminum is more negative and easy to displace in electrolyte solution. The zinc layer is sandwiched between the base metal and the silver coating to enhance the bonding strength between the coating and the base metal.

In the process of silver plating of aluminium machined parts, we should pay attention to the following points:

1) whether it is degreasing or alkali washing, the content of NaOH should not be too high, and the time should not be too long, so as to avoid surface corrosion.

2) the process of dipping zinc is the key to satisfactory plating. Zinc is to be dipped two times, because the zinc layer is coarser after the first dip. With 1:1 HN0, after its removal, do the second dip zinc. After second times of zinc dipping, only when the zinc layer with good consistency and fine bonding with the matrix can be obtained, the next process can be carried out.

3) During the process of zinc dipping, it is necessary to pay attention to the oscillation and prevent the parts from overlap with each other, resulting in a local zinc free layer.

4) If you find the quality of immersion zinc is not good, with 1: 1 HN0 removed, and then re dipped into zinc.

5) after the zinc dipping,the parts enters the cyanide copper plating solution, must live into the trough, and uses the high current impact plating 2min, then returns to the normal current. In electroplating, if the part surface is found black and dark, the parts can be removed then plated after treatment.

6) After the aluminum parts are plated with copper, they can be carried out according to the normal process of silver plating of copper parts.

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