Just don't pay attention to
@BoomStick , he's having yet another bad day it seems. There's no point in trying to remove oxidation from aluminum, as it is a highly reactive metal type that oxidizes immediately the moment when it comes into contact with oxygen from the air, and, the resulting thin layer of aluminum oxide is what protects the metal against corrosion. But this protective layer can still be penetrated (under some specific circumstances actually much more easily than many think........) due to atmospehric corrosion. See:
http://www.electrochemsci.org/papers/vol6/6126567.pdf
So, each time when atmospheric corrosion punctures the protective layer of aluminum oxide, the bare aluminum underneath spontaneously immediately oxidizes, after which it corrodes again, oxidizes again, repetitively and so on, digging deep holes not wholly dissimilar to how
@BoomStick keeps digging himself into deep holes all the time.