Q. I am plating aluminum with electroless nickel. When the finished part is subjected to the salt spray test, the coating blisters and pits are formed on the underlying aluminum. Is there a special process for plating electroless nickel on aluminum? P.N.P.
A. Plating on aluminum is not a “slam dunk” process. Aluminum readily forms oxides on the surface. These oxides protect the underlying metal, but they must be removed prior to plating of the surface. If they are not completely removed, you have peeling and pitting of the surface. I would guess that this is the cause of your problem.
A typical process for electroless nickel plating on aluminum and its alloys is as follows:
Hot degrease aluminum (60oC, 5-10 min.)
Rinse thoroughly (room temperature)
Acid pre-etch (50oC, 1 min.)
Zincate (room temperature, 1 min.)*
Strip zincate layer (dilute nitric acid)
Zincate a second time
Electroless nickel plate
*The zincate process involves replacing the aluminum oxide on the surface with zinc. You can find a lot more information on the zincate process by searching “zincating” on pfonline.com.
An alternative product for passivation...
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