Oxides form on the surfaces of metals because in the atmosphere they are in contact with oxygen. The nature of these oxides affect how we think of the metals themselves. For example everyone knows that if you leave iron laying around, it will get rusty.
The oxide layer on aluminum is very thin and adheres to the aluminum, insulating it from air and protecting it from oxidizing further. This is why we think of aluminum as a material that doesn’t corrode. (By the way, this aluminum oxide is the same compound that many gems are made of.)

Oxides form on the surfaces of metals because in the atmosphere they are in contact with oxygen. The nature of these oxides affect how we think of the metals themselves. For example everyone knows that if you leave iron laying around, it will get rusty.

The oxide layer on aluminum is very thin and adheres to the aluminum, insulating it from air and protecting it from oxidizing further. This is why we think of aluminum as a material that doesn’t corrode. (By the way, this aluminum oxide is the same compound that many gems are made of.)