Zinc does not rust, as rust is caused by a chemical reaction between iron and oxygen. This reaction produces ferric oxide and ferric hydroxide on the surface of the metal. Only iron and its alloys are capable of rusting.
Because zinc does not rust and is resistant to other forms of corrosion, it is used to coat iron and steel surfaces. The iron or steel is dipped into molten zinc, painted with zinc or electroplated in a zinc solution. The resulting metal is called galvanized iron or galvanized steel.
Galvanized iron and steel eventually rust, unlike pure zinc. Acids and salts in the environment eventually corrode the zinc, leaving the iron-based metal underneath vulnerable to rust.