Metal finishing Q&As since 1989

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Removal of tiny Aluminum bits embedded in Anodization

2005

I am currently procuring Aluminum 6061-T6 heatsinks from several machine shops.
These heatsinks have selective anodization and some are post-machined after being
fully anodized. Anodization is for purposes of electrical isolation. The heatsinks
end up loaded with high cost electronics.

In some cases, I receive these heatsinks from the machine shops with small bits
of aluminum embedded in the anodized finish due to fixturing from post-machining
and for other reasons.

I would like to find a way to remove these small bits of aluminum or make them
nonconductive.

I'm thinking that NAOH might etch the aluminum back out of the anodization, or
some type of acid like sulfuric, might oxidize these shiny bits to make them
noncductive.

Any advice or suggestion would be appreciated.

Russell Pate
electronics - Malabar, Florida

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My suggestion would be to instruct your machine shop to make sure their clamping fixtures are clean prior to machining your heatsinks. We do alot of maching, post anodization, at my place of work and don't have this problem. We do get aluminum scrape marks, but these are easily removed with Scotchbrite. Also, I find it puzzling that aluminum chips can be embbedded in AL2O3 (without severely damaging the coating), as the latter is much, much harder. Unfortunately, most of the chemicals that attack AL, will also attack the coating. Once again, an ounce of prevention is worth a pound of cure, tell your machinists to keep their stuff free from chips!

Marc Green
anodizer - Boise, Idaho
2005