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Anodized Al356 is corroding

2004

I have a automotive die cast AL356 component in development that has prolonged exposure to water and temperatures around 60 °C (but also dormant periods with the temperature being the surrounding ambient of 10-25 C). We currently have a 'light' or soft anodizing on the part. Recently we have noticed a white corrosion (aluminum hydroxide) with small amounts of sulfur and phosphorus mixed in that is present. Earlier prototypes of the part did not manifest this corrosion. We are in the process of comparing the anodizing 'thickness' between the two vintages but do not have the data at this time.

Any suggestions as to why the corrosion is occurring and how we can improve the resistance.

Thanks,

Daryl Harris
1st tier automotive - Auburn Hills, Michigan

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Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 26, 2008

Hi, Daryl. I think you are on the right track, that the coating may have been thicker or better sealed on the original parts.