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7075 Al pitting problem

May 19, 2008

The parts are screw machined ,degreased ,solution and aged heat terated. The pitting shows up at the cleaning process at Deox.

Please wtite possible solution.
SEM analysis of the pitted area reveals s, and chlorine peaks.

Thanks,

Ejaz Ilahi
Metallurgist - Jenkentown, Pa, US

May 20, 2008

When 7000's are heat treated or aged for a long time, the zinc migrates to the grain boundaries, then those grain boundaries on the surface let the zinc solublulize and float away. I have not heard of it showing up in the cleaner and deox, but it sure will "de-plate" away in the anodizing tank and leave small pits, and there is nothing youy can do about it.

Sometimes a very slow ramp will help.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

Ejaz

If you allow 7075 to sit in tap water (chlorinated) for an extended period of time, pitting can occur. This could occur in your post machining cleaning or post HT cleaning.

Willie Alexander
- Colorado Springs, Colorado
May 21, 2008

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