Ask the Expert Question-and-Answer Archive

by Ron Joseph

June, 2006

Zinc Phosphate Pretreatment of Aluminum

Q. If I zinc chromated a piece of sheet aluminium, would the appearance change in any way? I had a small job zinc chromated recently and the job came back to me looking exactly the same as when I sent it away.

A. First, I presume you meant to write about zinc phosphate and not zinc chromate. The zinc phosphate process does nothing for aluminum other than degrease the surface. The process is intended for steel in which case a dark gray coating is deposited. There is no reaction between the zinc phosphate and aluminum.

If you need to pretreat the aluminum prior to painting or powder coating, you should apply a chromate conversion coating, such as Alodine, Chemfilm, or equivalent.

Best wishes,

Ron Joseph