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topic 4822

Al 2xxx Surface Treatments


Is anodizing or alodining the best surface treatment for a 2000 series Al alloy that will be a sealing surface? Silicone o-rings will be used in the treated grooved alloy. Should the mating surface be anodized as well?

Also, is it difficult to process (i.e. surface treat) large parts (14 ft. diameter alloy rings)?

Brian Mayeaux
- Houston,Texas, USA


To anodize such a part you need a very large tank. Companies like Boeing have them, but not many jobshops will. Alodining (a trade name for MIL-C-5541 chromate conversion coating) can probably be done via brushing if necessary. There was a time when the external fuel tanks of the shuttles were chromate conversion coated (I don't know if they still are) and they are obviously very big.

I don't know enough about it to give a dependable answer, but I personally don't know any reason the Alodine should be unsatisfactory. Ted Mooney, Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

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