Aluminium as we know it is the oxide. Al is very reactive and oxidises almost immediately on on contact with air, but the oxide is very stable, and unlike iron (rust) doesn't flake off etc, so the 'oxidation' of Al is nothing to be worried about.hd reynolds said:Aluminum oxidize.
On another note, you can leave titanium outside with the elements for a 100 years and it will look the same as the day you left it