Why does aluminum resist corrosion in air?

Although aluminum is a chemically active metal, it is highly resistant to corrosion when exposed to air. This resistance occurs because a hard, tough oxide film forms naturally on the metal's surface.12

This thin layer acts as a protective barrier, isolating the underlying metal from the environment and preventing further oxidation. While this film forms spontaneously, its thickness and protective qualities can be further enhanced through a process known as anodizing, where the aluminum part is made to function as the anode in an electrolytic cell.2