I doubt there's anything wrong with the metal; the problem with cans is that they have a coating on the inside to keep the liquid out of contact with bare alumi

I doubt there's anything wrong with the metal; the problem with cans is that they have a coating on the inside to keep the liquid out of contact with bare aluminum. Obviously, it's pretty hard to separate the two without melting the can completely. The outside of the can, of course, has paint on it. The tabs are pure aluminum without any protective coating or paint.