Metal finishing Q&As since 1989

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Pitting on cast 356 hard anodized Aluminum Alloy

Hello, I work in the steam oven industry and recently there have been problems with a cast, hard anodized 356 Aluminum alloy part pitting on the inside of the oven. The cast part makes up the inside walls of the oven so it is constantly in a high heat and high humidity environment and likely exposed to all kinds of salts and acids from steaming different foods. I have read from different sources that high heat can cause anodized coatings to form very small cracks which would explain the pitting, but then at the same time anodized aluminum cookware is very popular which also experiences high heat and is directly exposed to salts and acids from foods so I am confused why the same doesn't happen to cookware. Any advice on what might be causing this pitting in the cast part mentioned above would be greatly appreciated and please don't hesitate to ask if more information is needed. Thank you in advance.

Sean Donovan
Product Designer - Burlington, VT, USA
July 10, 2009

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I would look at the quality of the original casting. Extrusions are a some time problem and cheap castings, especially imported ones, are normally a serious pain.

Even investment casts can sometimes have flaws.

James Watts
- Navarre, Florida
July 13, 2009