Ask the Expert Question-and-Answer Archive

by Ron Joseph

June, 2006

Zinc Chromate for Corrosion Protection of Aluminum

Q. I have been reading some of your responses to Zinc Chromate protecton of aluminum stuctures. We build aluminum trailers. My question is weather we should treat our trailers with Zinc Chromate to make them last longer. I have been told that the aviation industry is big on these coatings but is it comparible to a aluminum suspension on a heavy trailer that is exposed to a wet and sometime corrosive invironment?

Most of our trialers also have steel suspensions attached to aluminum frames. We currently do a minum job of galvanically seperating these parts. Can you suggestion a coating that would work in this area as well.

Thanks for any help you could give me.

A. I don't know if we are on the same page. Aluminum should be pretreated with a chromate or non-chromate conversion coating, both of which are multi-stage aqueous processes. This is NOT the same as a zinc chromate primer. For the type of trailers that you produce I strongly suggest that you consider the pretreatment before applying your primer and topcoats. Zinc chromate in the primer is advantageous, but with the new hexavalent chromium rule in place (as of May 2006) you might want to review this before going forward with a chromate-containing primer. What type of coating system have you been using in the past? Have you had success with the system? Why are you thinking of changing?

Best wishes,

Ron Joseph