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Problem Replating Electroless Nickel on Aluminium

Hi,

Please help me to overcome a problem I have obtaining a particular Litton style connector used in the Rail industry. I am involved with build of a braking unit for the train and the required specification for inclusion of this connector is proving difficult to overcome.

I have been unable to obtain an aluminium connector type with Electroless Nickel plating. A connector plated with green zinc cobalt was available and these were bought with the intention of stripping and replating with the required finish.

The green zinc cobalt finish has been removed using Nitric Acid but unfortunately a dark residue remains spattered about the connector. This appears to be "pitting", which I understand needs to also be removed. How should this be removed so that the Electroless Nickel plating can be applied on clean aluminium base material?

Thanks in advance for any respondents, it's much appreciated.

Robert McCausland
Engineering - Bath, England, United Kingdom
February 27, 2009

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March 4, 2009

Robert,

It sounds as if there is some smut on the surface of the aluminium. There may well be some pitting but this would generally be associated with the base material before plating as nitric acid has a minimal effect on aluminium (assuming you are not leaving it soaking in the acid for hours). The way to remove this is usually by dipping in a chromated deoxidiser solution, these are self desmutting.

The parts should then be double zincated (zincate, strip zincate and then re-zincate) before plating. I usually nickel strike the parts before plating, I find you get a better key, but I know of people who go straight for plating on top of the zincate.

Your best bet is to contact a local plating house that offers electroless nickel and let them do all the cleaning, etching and plating for you. Just make sure you clearly explain what you want.

Brian Terry
Aerospace - Yeovil, Somerset, UK