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Zn-Ni alloy stripping

In stripping of electroplated Zn-Ni deposit, we alway found black ash on surface and this ash can only be removed by rubbing. Is there any cleaning method can remove this black ash?
Thank you for helping.

John Su
Engineer - SHENZHEN, CHINA
February 14, 2008

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You haven't told us about your situation, John, so that we can guess what the black ash is and how to prevent it or remove it chemically. How do you strip the parts, what are they made of, is the stripping electrolytic, what is the solution, is it done on racks, in plating barrels, or in bulk?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
February , 2008

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February 17, 2008

Originally we would like to strip off the bad quality Zn-Ni plated (13-14% Ni) articles (Rack) by 50% HCl, but we found that the surface was covered by a layer of black ash even long time dipping in the acid. Soak cleaning and Electro-cleaning (anodic) seem no help to remove this black layer. The only way we found to remove this layer is by rubbing and so we would like to know if anyone can suggest us an alternative method to remove this layer easier.
Thank you.

John Su
- China

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I have only a hunch, not facts, but I suspect that the plating is stripping off easily but in the course of doing it you are causing the substrate to get smutty by too heavy an acid treatment. Try reducing the concentration or immersion time.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
February 21, 2008