Metal finishing Q&As since 1989

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Anodising problems

I am working in anodising plant as supervisor.plant located at Chennai. we are using a 20% sulfuric acid at 20deg for anodising . we are having an Al alloy 5%Cu,12%Si. We are facing a problem in finish. FInished material having greenish in some area. I feel that cu is also oxidised. I thought alloy was etched during process. Another one is roughness. which is best method const current or voltage.

M.Ramasami
- Chennai, INDIA
2006

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What casting & cleaning processes?

This alloy (a bit more alloyed than 384) isn't expected to give a good anodized appearance. Avoid caustic etching -- use only as necessary to hide scratches, etc. Caustic preferentially attacks the aluminum, increasing the surface Si & Cu content. Use a fluoride-containing deox/desmut.

Constant anodizing current is preferable.

I've heard that burnishing can homogenize the surface to enable a good anodize appearance. Anyone know more about this?

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2006