Aluminum metal is not attacked by air or water and thus not corroded, although it occupies a high position in the reactivity series. The reason is

Aluminum occupies quite a high position in the reactivity series of metals, So it is expected to be very reactive and get corroded readily on exposure to atmosphere. But it is not so. Actually, when aluminum metal is kept in air, it combines with the oxygen of air to form a thin, but strong layer of aluminum oxide on its surface. This layer of aluminum oxide is unreactive and protects aluminum metal from further corrosion. So the oxide layer reduces the chemicaI reactivity of aluminum. Thus, the aluminum metal is not attacked by air or water due to the presence of a protective layer of aluminum oxide on its surface.