Adhesion of Powder to Anodized Aluminum

Q. I read the comments made to the question of adhesion failure on aluminum in the January 2011 issue and would like to get your opinion as to using anodizing as a bonding layer for the powder coating or a wet paint application. C.B.

 

A. An anodized aluminum surface is usually used without an organic topcoat. However, some companies want the great corrosion protection from the anodizing and the decorative look of the coating.

I have had inconsistent results with adhesion over anodizing. I am not educated on all of the variables in the anodizing process, so I do not know what impacts adhesion. When it works it is a great finish, but in many cases the anodized surface is not good for powder or liquid bonding.

I would that you do some wet adhesion testing as outlined in AAMA 2605 (American Architectural Manufacturing Association). You do the test the same way as a dry adhesion test per ASTM D3359 (American Society for Testing and Materials) but you place the panel in boiling demineralized water for 20 min after you make the cross hatch cuts and then do the tape pull after the boil. If you can pass that, you probably have a good part