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[VACList] Re: VACList Digest V3 #273 - Stainless screws in aluminum
They don't rust, but what they do is cause corrosion of the aluminum. Stainless
(nickel-chromium-iron alloy) is higher on the electromotive potential scale
(hadn't thought of that since college 30 yrs ago!) than aluminum, which results
in the aluminum corroding instead of the screw.
Cadmium plating has been used for a long time on steel screws and cold set
rivets that are in aluminum. In practice, until the cad plating is all gone, the
aluminum is protected and so is the steel.
Aluminum screws and rivets are most compatible with aluminum, though due to
differences in alloys between screws and rivets and aluminum sheet, that may be
a slight degree of corrosion.
We can get away with stainless in aluminum in inland regions but in coastal
areas the salt air really goes to work on that aluminum especially if stainless
screws and rivets are used. Stainless is never used (or should never be used) on
boats for fastening aluminum.
When I lived in Palm Beach I noticed that the aluminum screens were "fuzzy" and
there was quite a deposit of aluminum corrosion powder on the window sills. The
aluminum window frames were heavily pitted.
Al Grayson