Ask the Expert Question-and-Answer Archive

by Ron Joseph

April, 2005

Corrosion of Dissimilar Metals

Q. I do understand about battery action in dissimilar metals but I had no choice but to use this combination on my aluminum sided trailers (well I did have a choice but it is too late now). I plan to use zinc chromate primer and automotive enamel for a finish coat (which is how I was taught by the Air Force) but because I understand that I am 30 years out of date in my training (or God Forbid, have a bad memory), I am asking for your advice.

A. Your memory is better than you give it credit. Are you painting the galvanized screws on one trailer or on a production line of trailers? For a single trailer you should be OK with the paint scheme you suggested, but insure that the screws are well covered so that moisture does not penetrate through top the aluminum substrate.

If you are using this approach on a production line, then you should give this preoblem more consideration, because sooner or later you will have customer rejects. An alternative solution might need to be developed.

Best wishes,

Ron Joseph