Metal finishing Q&As since 1989

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Anodizing on investment casting parts made of 356 Alloy?

2006

Q. I was told that investment casting alloy 356 cannot be anodized because it would contaminate the anodizing bath?
Is this correct and if so, what would be the best (low thickness dark color no gloss) finish for this alloy?

AA 356.0
Category Aluminum Alloy
Class Cast
Composition

Element Weight %
Al 92.05
Cu 0.20
Mg 0.35
Mn 0.10
Si 7.00
Fe 0.20
Zn 0.10

Thank You,

Gérard Blais
electronics systems - Canada

A. 356 Castings can definitely be anodized - we do it here daily.

Because they are not pure aluminum, you will not get a pretty looking, decorative finish, but they will be anodized.

David A. Kraft
- Long Island City, New York
2006

A. I do not buy the "it will contaminate the bath" comment. Some anodizers do not like to anodize cast materials as castings are not easy to anodize and there are a lot of bad castings, which look ugly after anodize, even hard anodize.

James Watts
- Navarre, Florida
2006

A. You see there is a lot Si in your Element Weight List and will get a blackish Anodized Layer after sulfuric acid anodizing with something silicon content on the semifinished surface. So if you wanna a better and homogeneous anodizing layer, remove the silicon and little copper on the surface of Aluminum Alloy before the anodizing job running.

Jason Xu
- China
2006

I thank You all for the answers, I will proceed with the anodizing for this project.

Gérard Blais
- Dorval, QC, Canada
2006