Letter 4042

How to black dye aluminum castings. 

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How should an aluminum die casting be anodized in order to dye it black.

I've heard of a pretreatment using hydrofluoric acid with something else that will remove part of the silicon in the surface so you can get a clear coat that can be dyed. Does anyone knows how this works?

Guillermo Luna
Compañia Estañadora Nacional, S.A. de C.V.

Mexico City, Mexico

March 1, 2009

Hi, Guillermo. Aluminum diecastings can be anodized and dyed black, but the purer the aluminum the better it can be anodized. Silicon and copper cannot be anodized, so the part is desmutted in an acid that can dissolve these before it is anodized.

Yes, a mix of nitric and hydrofluoric acid can probably successfully desmut die castings, but greater consistency and safety can be achieved by using a proprietary acid salt than raw chemicals. Good luck.

Regards,


Ted Mooney, P.E. 
finishing.com
Brick, New Jersey

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