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-----Galvanic potential between zinc and nickel plated parts
Q. We are having trouble with nickel plating (EMI reasons) on some electronic chassis. One part was changed to zinc plating. What is the galvanic potential between the nickel and the zinc? Will it be a problem? What can be done about it?
Scott Long- Pittsburgh, Pennsylvania, USA
2002
A. Hello Scott.
Galvanic corrosion requires 1) a conductive metal path,
2) a difference in electrochemical potential between the two metals, and
3) an ionic path.
There is a significant difference in electrochemical potential, so you need to address the problem through point 1 or point 3.
Point 1 means adding insulators so that the nickel never actually touches the zinc, no metallic path.
Point 3 requires keeping the parts clean and dry. If the equipment is installed in a controlled, clean and very dry environment, point 3 may eliminate the problem without having to do anything about point 1 or 2. Good luck.
Ted Mooney, P.E.
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finishing.com - Pine Beach, New Jersey
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A. Scott,
Electromotive force series seldom applies in the real world but it shows exact potentials measured under strict and standardized conditions. Galvanic series is an average "real world" list of the position of metals and alloys according to their tendency to corrode. Nickel (specially if passive) is so much apart from zinc. I wouldn't be surprised that you had around 1.0/1.5 Volts in your case.
Monterrey, NL, Mexico
2002
Q. I have a customer using an electrolytic nickel plated steel bolt into a zinc diecast nut. Occasionally they are seizing up much like a stainless steel fastener does when it galls. Does this type of plating typically do this and do I need to consider adding a lubricant to the bolt after nickel plating it?
Steve Selle- Painesville, Ohio, USA
June 24, 2013
A. Hi Steve. This is a troublesome design, especially if used outdoors where moisture could become an issue. The zinc nut is a sacrificial anode. Lubricant might help, but I think you need to either nickel plate the nut or zinc plate the bolt instead of nickel plating it. A bright acid zinc plated bolt will have at least some degree of shine initially.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
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