Greg...
Carrying that thought further, any aluminum bussing installed near the ocean is at hazard for AlCl3 'rust.'
Aluminum is normally considered 'rust proof' because run-away corrosion does not occur -- unless chloride ions are present.
But, aluminum is, in fact, prone to ultra-rapid 'rusting' / oxidation. Bare aluminum metal oxidizes promptly in air. It acquires a THIN coat of Al2O3 -- aka alumina. It's so thin that you can see right through it. Unlike iron oxide rust, alumina expands to lock up tight, creating an air tight seal.
If salt air is misting in, the chlorine displaces the oxygen in the alumina. Now the metal loses its sheild. AlCl3 shrinks like common rust. Given enough time, aluminum metal becomes pitted -- with cruddy AlCl3 ( it's yellow ) crystals at the surface.
I've witnessed bussing that's picked up a 3 volt drop right at the rails (under load) over a twenty-year period.
The solution is to kill power, buff the crud off the rails, clean the breaker-rail contacts and re-assemble.
Where it's an issue, copper bussing is worth the premium. Copper does not rapidly react with salt air like aluminum.
This issue is why aluminum can't be totally trusted below grade. Some American soils are absolutely laden with old ocean salts. (Nevada, California, Utah, Arizona,...) So you can't trust aluminum to stay bonded as part of a GEC system.
