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Galvanic action between chrome, steel and aluminum

We have aluminum parts and steel parts that need to be masked and chrome plated in defined areas. After plating, chrome and bare metals could get exposed to outdoors environment. Paint may not be an option because of high temp (400 to 500 F) requirement. What will be the effect of galvanic action, and how to prevent it?

Mandar Sunthankar
- Fort Collins, Colorado
2002

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2002

This is obviously trouble. The steel or aluminum would corrode even without the chromium present; with it there the corrosion rate will probably increase significantly. The aluminum should corrode at record speed.

Any chance you can electroless nickel plate the whole part before selective chrome plating? Even copper plating it would help.

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

Ted, it may be possible. However, could EN or copper prevent corrosion on both steel and aluminum? What about effect of a scratch or wear on copper? Any effect of pinholes?

Mandar Sunthankar
- Fort Collins, Colorado
2002

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I don't know enough about the application and its requirements to be able to talk about it except very broadly. But aluminum is a very active metal, so I was assuming that you won't be able to protect it cathodically, and will instead need a barrier layer coating. Nickel is the most obvious choice; I mentioned copper as an alternate only because I have no idea whether nickel is satisfactory to your other needs. Yes, it must be pinhole free, but that's not an unusual requirement; lots of aluminum is nickel or electroless nickel plated

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002

I believe we are making major general statements here. What is the corrosive media? Are we only worried about atmospheric corrosion and rain? Aluminum is always found as aluminum oxide and if it is in touch with steel, no galvanic should not be significant. Atmospheric corrosion does affect steel but a high conductive environment or aqueous solution (acidic or basic is required). One must also take into consideration the effect of anode to cathode (Chrome or Al) before predicting the corrosion tendencies.

Kam Dianatkhah
Lennox - Dallas, Texas
2003