Metal finishing Q&As since 1989

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Can we Chem Film (Chromate Conversion Coat) aluminum without deoxidizing

I seem to have a problem sometimes when we Chem Film parts with holes, that they have excess deoxidizer in the hole that causes a run-out on the chem film. My question is do I have to use a deoxidizer or can I just hot alkaline clean and hot water rinse and then chem film to stop this problem? I ran some sample's and the parts look acceptable without the deoxidizer step.

Kevin Duncan
- Los Angeles California
2000

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If the parts are scrupulously clean, and you get the same results (not merely acceptable) without it, I would document it in my quality program, and run them without the deox. It depends upon the purity of the aluminum; the more pure, the less you need the deox.

  
Tom Pullizzi
Falls Township, Pennsylvania
2000

We have found that the deoxidizer used has an effect on passing the salt requirements of MIL-C-5541. The lack of a deoxidizer may compound the problem.

WILLIAM F. MORGAN
MFG AND ELECTRONICS - SARATOGA SPRINGS, NEW YORK, USA
2000

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Hi, Kevin.

As an aid to understanding, please recognize that although this step is widely called "deoxidizing", it's not deoxidizing, it's desmutting -- it's the removal of copper, silicon, and/or other non-aluminum materials from the surface.

So, as Tom notes, the more pure the aluminum, the less necessary. And as William notes, the salt spray performance is likely to suffer if you're leaving that copper there. One more note, then, would be that if you etch, or over-clean, desmutting becomes more necessary. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
March 31, 2011