It's mostly moisture being trapped under the paint.
Aluminum is extremely sensitive to oxygen. If it didn't corrode so fast, it would burst into flames in air.
So, as the previous poster said, you can salvage them. You'll have to completely strip the old ones, clean off the residue, and either lacquer or paint them. If you just strip the paint off and polish, they'll still be fine as wheels, but they'll look dirty very quickly, and no clue what the brake dust would do to them.