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topic 61089

Stripping zinc nickel passivated with black hex from electroless nickel/aluminium




April 7, 2020

Q. Hello,

I am Elie, I work as an electroplating engineer in a connector manufacturing facility, I am looking at how to strip an alkaline zinc nickel coating from an electroless layer on aluminium connectors.

We plate aluminium connectors with mid phos electroless nickel (around 10 µm) and plate zinc nickel that we passivate using a black hexavalent chromium based passivate.

My objective is to strip the zinc nickel layer from the electroless nickel without damaging either the electroless nickel layer or the aluminium part and without using current.

I am trying to avoid having to strip the electroless nickel as we lose some dimensions when we have to rework it.

I would be happy to receive any suggestions on how to do this.

Elie Marchal
engineer - England / Kent


April 2020

A. Hi Elie. Plating zinc-nickel on top of electroless nickel, let alone stripping just the zinc-nickel and chromating conversion coating sounds rather unusual, and I'm not familiar with it. A hot caustic, similar to a soak cleaner for steel ought to remove the chromate and the zinc. I don't think it will damage the electroless nickel per se but if there is any porosity or pinholes (and at 10 µm there may well be) it would destroy the aluminum, and even if it doesn't, how can you re-activate the electroless nickel without a Wood's Nickel strike?

If the parts aren't precious you can experiment with a couple and try stripping them with hot caustic. Or you can wait for an answer from somebody who has a better idea :-)

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading


April 9, 2020

thumbs up sign Hi Ted,

Thank you for your answer, we do this on connectors for mil/aero applications, this is a bit of a niche market I imagine.

I have plenty of parts that are low value so I can give it a try, at the moment we use fluoride based salts to re-activate electroless nickel (as recommended by our chemical supplier) but that's normally electroless nickel that was plated at most a few hours ago.

Elie Marchal [returning]
- Kent, England


April 2020

A. Hi again. In the "dirty old days" of metal finishing which I saw in a number of shops, when zinc plated and chromate conversion coated steel parts were rejected, no real thought was given to a stripping protocol, they were simply run through the line again with the raw parts ... the soak clean tank would remove the chromate and the zinc, and certainly the acid dip instantly removed any traces of zinc if there was any left over.

All I am actually relating to you is my guess that zinc-nickel plating can be easily removed with the same chemistry :-)

Luck and Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading

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