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Powdercoating aged alodine

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I have conversion coated surfaces that I would like to powdercoat. The conversion coating has been on for 6-12 months. Does this have to be removed to get good adhesion to the aged surface? Will I still get good corrosion protection?

AJ Nielsen
- Duluth, Minnesota, USA

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Six months room temperature low humidity shelf life should not matter provided you can remove the organic soils that may have settled on the surface.

More important, especially with powder coat, is that the chromate conversion coating be very thin. If the chromate is too thick the coating will sheer and the paint peel right off. Also, if the coating is thick, the high temperature of curing powder paint will crumble the chromate and, again, the paint will peel.

Robert H Probert Robert H Probert Technical Services Garner, North Carolina Editor's note:        Mr. Probert is the    author of Aluminum How-To / Aluminio El Como

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I have some parts that I want to powder coat in some areas and alodine in others. I need the alodine for corrosion resistance and conductivity and the powder coat for corrosion resistance and aesthetics. How should I go about getting this combination? Can the powder coating be subjected to the processes required for alodine coating? If so, how does this affect the powder if at all? Also, if a part is alodine coated, then powder coated, and the re alodined is the second alodine coating as good as the first? What kind of dimensional change could I expect from two coatings of alodine? Any information will be much appreciated.

Thanks,

Brian Atchley
- Santa Rosa, California, USA