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Large underwater vehicle chassis - to anodize or not to anodize?

I have a large 6061 Aluminum welded chassis for an underwater vehicle (for use for up to 10 days in saltwater). The part is roughly 1000 lbs, made up from angles, flat plate, and box tubing. Fasteners are SS, but isolated by plastic.

Should I anodize the chassis, or leave it bare and add zincs? My concern with anodizing is if the chassis gets scratched or nicked, that the potential would be considerably higher than if I let the entire frame "corrode" as one piece. The unit will have a thorough fresh water washdown after each use.

Any recommendations?

Thanks!

Tim Curtis
Designer - Largo, Maryland
2007

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Hi, Tim. I don't think I agree with your analysis about a nick corroding faster than an unanodized chassis. That problem would develop only if the nick exposes a more noble material or there is a more noble material present in the circuit. If conditions are such that the zinc anode corrodes preferentially to the aluminum, then the smaller the exposed area of aluminum it must protect, the better. Remember that the zinc must touch bare aluminum though.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007