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Gold under Nickel

We've recently been removing some nickel plating (not sure if its EN, or not) for a customer, using nitric acid/water mixture. We came across a part that had what appeared to be gold underneath the plating. SEM analysis confirmed it was AU. Is this a standard process in any kind of nickel plating? If so, what would the purpose of the AU be?

Marc Green
anodizer - Boise, Idaho
2004

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2004

Marc,

I can't imagine any reason to plate Ni over Au, unless it is to provide a time delay in a corrosive environment to Ni.

James Totter, CEF
- Tallahassee, Florida

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A most unusual thing to find! Most people plate gold onto nickel. Marc, what is the substrate and the role of the component? It is just possible that the gold is there to act as a diffusion barrier to prevent the nickel migrating into the substrate. However, I can think of cheaper barrier layers, unless the end-use demands something like gold.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2004

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First of three simultaneous responses --

Certainly unusual, but not so much if you are familiar with Marv Rubinstein's "know-how" [Electrochemical Metallizing]. We have done thin layers of high phos EN-over thin gold-over nickel strike to protect critical alloy steel components subject to hot chloride and wear conditions. Nickel strike provides adhesion to substrate, gold midplate impedes further penetration of corrosive gases through pores or voids in the outer nickel, whereas the later protects gold from abrasion. This combination, which works very similar to copper-nickel-chrome but much thinner (0.0003-0.0005")proved to outlast single high phos EN, TiN and other competing thin coatings.

Guillermo Marrufo
Monterrey, NL, Mexico
2004

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Second of three simultaneous responses --

There's some work done at the University of Florida in the 1960's by a Dr Rhines. He was studying gold as a diffusion barrier to metals and he was also studying the use of gold as a barrier to Hydrogen Embrittlement.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2004

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Third of three simultaneous responses --

Hi Marc,

I suspect this rather to be an unsuccessful first plating attempt. The article was gold plated, did not look good and was sent back to nickel. I cannot think of one reason for gold plating under nickel.

All the best,

Trudy Kastner
electroplating service - Durban, KZN, South Africa
2004

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Thanks for all your input, guys. The part itself, is aluminum, and is used in the semiconductor industry for wafer processing. The end user was very surprised that the gold was under the nickel, as gold is very harmful to wafer manufacturing. I guess this one will remain a mystery, as it doesn't sound like this is common practice.

Marc Green
anodizer - Boise, Idaho
2004