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Galvanic compatibility of Brass to aluminum and aluminum to galvanized steel

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
2003

Hi Dean.

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.

As someone who has moved washing machine, and consequently had to "unscrew" aluminum hose fittings from a brass faucet, the answer to your first situation is: 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 non-critical 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. Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003