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Letter 24046
Brass/aluminum and aluminum/galvanized
steel compatibility
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Please advise on compatibility for anodized aluminum female
threaded onto brass. Also, please advise on compatibility for
anodized aluminum flanged joint with galvanized steel employing 316SS
bolts/nuts.
Dean Ratzlaff
engineering company - Bellingham, Washington
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The short answer is that dissimilar materials are always
galvanically incompatible.
How incompatible depends on the environmental conditions, the
separation of the two metals on the sea-water series, the criticality
of corrosion, and the exact details of the connection.
Anyone who has moved a washing machine, and consequently had to
unscrew aluminum hose fittings from a faucet, will know the answer to
your first situation: completely incompatible! Unless you consider
removal with the aid of a hacksaw acceptable :-)
The second situation doesn't sound nearly as bad and could be
perfectly satisfactory in certain situations. I see galvanized steel
coupled to anodized aluminum in all kinds of non-critical outdoor
situations like walkways, stadium seats and rails, etc. The stainless
screws could cause some localized pitting, but it may not be a real
problem at all.
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Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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