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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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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.

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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).

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