Letter 2015

Is anodizing or chromate conversion coating better under powder coating

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I am trying to find answers to the following questions:

1. Is the adhesion of powder coatings on aluminum improved by anodize or alodine treatment before coating?
2. If there is an improvement, is there a significant difference between the two treatments?

I also would like to know, in simple terms, what the difference is between anodize and alodine.

Can any of your readers help?

Marshall Davidson
- Meriden CT

Alodine is a brand name for a process which is generically called chromate conversion coating. These coatings are electrically conductive and corrosion resistant but with almost no abrasion resistance.

Anodize is an electrochemical process which converts the surface aluminum into aluminum oxide. It is non-conductive with significant corrosion and abrasion resistance.

Both coatings are widely used as adhesion promoters. However, some post treatments can cause adhesion problems. Make sure your finisher knows the final application. Generally, chromate conversion coatings are less expensive than anodize, while anodizing offers better protection.

Chris Jurey Luke Engineering & Mfg. Co. Inc. Wadsworth, OH

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