Alloy wheel corrosion

[C M Smith <cmsmith@domain.elided>]

I'm no metallurgist either but I do know that unprotected alloy wheels will 
corrode. Road wheels should be painted or clear coated or they will 
inevitably be disfigured by corrosion. In winter every little stone chip 
eventually gets a white/grey powdery look. Even if you have no winter, bare 
alloy will corrode eventually.

Dissimilar metals will speed the corrosion due to galvanic action. Less 
"noble" metals sacrifice to more noble. Aluminum and Magnesium are both 
sacrificial in the auto wheel environment (in fact aluminum is produced by 
applying powerful electrical currents to bauxite to extract the metal from 
the "ore") and so any wheel weights should be plastic coated.

Aluminum can be protected by the corrosion however, so substantial 
weakening of the wheel is very unlikely in the absence of serious galvanic 
action. The idea behind anodizing involves "corroding" the aluminum in such 
a way as to seal the surface from the air with a very hard surface which is 
essentially corroded aluminum. I don't know if any auto wheels are anodized 
but there's no reason it wouldn't work on wheels. Sailboats have used 
anodized aluminum alloy for many years without corrosion problems. Most 
modern alloy wheels are painted or clear coated.
Michael Smith
Calgary, Alberta
Canada
91 Alfa 164L, White, original owner

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