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Powder coating of zinc electroplated steel parts

We powder coat a lot of cold rolled steel and aluminum parts. Sometimes the steel parts need to be zinc electro-plated first, because the part needs to have area masking for electrical conductivity. We have experienced outgassing or something that causes bubbles and pinholes in the finish. What is the best way to preteat this substrate to get good results. Is preheating the right thing to do?

Alan Purdey
Wesgar Industries - Vancouver, BC, Canada
2000

I have experienced that before with alkaline zinc, and it was related to the thickness of the zinc plate, when we plated at .2-.3 mils it was ok, above .3 mils our customer complained about the little blisters. It was a bright finish and at the time I thought it might have been related to the entrained brighteners vapping out during the powder cure, but in any case cutting down the plating thickness to below .3 mils fixed the problem and we kept the job.

Ward Barcafer, CEF
aerospace - Wichita, Kansas
2000