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Galvanic corrosion: Zinc-Nickel plated steel in contact with copper

Q. Hi,

Zinc-Nickel alloy plated (Cr3+ passivated) steel failed with red rust at 96 hours which is contacted with copper metal part (Copper metal bolt + Zinc-Nickel plated nut.
Please anyone tell the reason for this failure.

Regards,
Divahar

Divahar Raja
Corrosion - India
January 19, 2012

A. Hi, Divahar. I'm almost not understanding the question because you have called it galvanic corrosion, and described the conditions that cause galvanic corrosion, and then asked why it happened :-)

Contact with copper in a salty environment will cause rapid galvanic corrosion of both zinc-nickel plating and the underlying steel.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
January 19, 2012

Q. Which finishing is suitable for steel, to avoid galvanic corrosion between Steel and Copper?
I'm expecting 250 hrs salt spray life in this combination.

Divahar Selvaraj
- Tamil Nadu, India
March 26, 2013

A. Hi Divahar. MIL-STD-889 has an excellent seawater series chart. Nickel plating is very close to copper on that chart, so there should be little galvanic corrosion. Of course, bare copper will get unsightly tarnish and you may wish to nickel plate everything. 250 hours is quite a bit. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
March 26, 2013

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