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Nickel Plating on Aluminium

We are trying to develop a SS finish on Aluminium Machined Pieces. They raw piece is machined out of an Extruded Aluminium Rod (Alloy 6063). On this piece we do Electroless Zinc after proper polishing and pre treatment with Nitric Acid (30:70 water). After that we do Cyanide Copper and then Nickel Plating (electroplating only). The piece is then buffed with a non - woven wheel to give it a Dull effect. The problem is the Nickel tends to peel off from places and the coating blisters also in various places. We also tried to avoid Cyanide Copper and do nickel directly after Electroless Zinc. This also does not help.

Please advise what could be wrong.

Thanking you in advance,

Chinmay Agrawal
- JAIPUR, India
2002

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First of two simultaneous responses --

If you need to get rid of the cyanide copper step, you can electroless nickel plate instead. But the separation isn't caused by bad theory it's caused by poor execution of the details. Cyanide copper on zincate will work. Don't forget to mechanically finish the aluminum, use a proper aluminum pretratment process, and double zincate (zincate, strip, re-zincate).

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002

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Second of two simultaneous responses --

First, you say "electroless zinc" over aluminum. Do you mean zincate? Yes? What is your chemical composition and what is your process in detail? Are you doing double zincate? Also, you say you do it after "proper polish". How are you polishing?

Guillermo Marrufo
Monterrey, NL, Mexico
2002