What many people don't realise is that aluminium is in fact a very reactive metal. The reason it appears to resist corrosion is that the aluminium rapidly oxidises and the oxide forms as a very thin layer on the surface of the metal. Aluminium oxide is pretty resistant to attack by acid materials, but not by alkalis. For this reason you should never put cookware in a dishwasher as dishwasher detergents are highly alkaline and the aluminium is attacked by the alkali.