[VACList] Re: VACList Digest V3 #273 - Stainless screws in aluminum

[<waymark1@xxxxxxxx>]

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