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Salt fog protection for different types of plating

Dear Sir,

I did plate a mild steel part with a silver plate (3 micron) over a electroless nickel plate (10 micron). When I send for the salt fog test, it found that it failed for this test. May I know is the nickel a good protection for the corrosion? What about if the plating spec change to cu-nickel-silver? Will this be better than the previous one as I did? Thank you.

CC Tang
plating house engineer - Malaysia
October 23, 2008

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Hi, CC. Salt spray testing is a QC measure meant to help assure that a successful plating process or specification has not deteriorated. It was never meant to indicate which of two different types of plating or coating is more robust in the real world, and it can't do that. Accelerated corrosion conditions are fundamentally different than real-world conditions, and anti-corrosion mechanisms that work in the real world, like the formation of films of tough carbonated corrosion products, won't form in the salt fog chamber.

I don't think an underlayer of copper will substantially improve the performance of an electroless nickel coating, but making it just a little bit thicker, and consequently less porous, might. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 23, 2008