Why do aluminum clad steel wires have high corrosion resistance despite being two dissimilar metals?
Does the aluminum act as a protective & sacrificial layer similar to zinc in galvanization or is there some other mechanism going on?
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2 Answers
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The dominant protection mechanism is that the aluminum excludes seawater from contact with the steel underneath, and if passivated with a layer of oxide, the corrosion rate of the aluminum via direct chemical attack will be low.
Aluminum does not protect steel the way a coating of zinc will. If the aluminum gets pierced and the steel underneath is exposed, the aluminum tends to get undercut via crevice corrosion and come off the steel.
answered Jan 21, 2019 at 23:12
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It has good corrosion resistance in dry air ( same as pure aluminum ).In an ordinary location with occasional rain it works well. Dissimilar metals is not a problem if there is no electrolyte ( eg. water). In wet conditions, especially along a sea coast (salt) corrosion will be significant. The aluminum is sacrificial protecting the steel , with a little more voltage than zinc. Offshore steel structures are usually protected with aluminum anodes. Although life is longer in sea water because a "calcarous" deposit builds up and stiffels corrosion ( not always, that is why there are galvanic protection engineers and contractors).
answered Jan 21, 2019 at 21:38