Aluminum does rust, but it rusts differently versus steel and iron rust. When aluminum is exposed to oxygen, it forms aluminum oxide, just like steel forms iron oxide, but the difference lies in the chemical makeup of these two oxides.
Iron oxide or rust is a soft red colored metal that begins to expand and flake off as it is chemically transformed. This process exposes more of the underlying steel to the air and the process continues until the metal is completely transformed to iron oxide.
Aluminum oxide has a different process. It’s actually quite hard and serves as a protective coating around the underlying aluminum. It doesn’t flake off like iron oxide. Once the outer layer of aluminum “rusts” the process stops and the aluminum is protected.