Rust
Rust is the chemical produced when iron compounds corrode in the presence of oxygen and water. It is a mixture of iron oxides and hydroxides. Rusting is a common term for corrosion, and usually is the corrosion of steel. The process of rusting can be summarized as three basic stages: The formation of iron (II) ions from the metal; the formation of hydroxide ions; and their reaction together, with the addition of oxygen, to create rust.
When metal is produced for automobiles it is galvanized with zinc coating for protection. Zinc is applied by either hot-dip galvanizing or electroplating. Zinc is traditionally used because it is cheap, easy to refine, and adheres well to steel. Zinc also provides catholic protection to metal that itself is unplated, but close enough that any water touching bare iron is also in contact with some zinc. In the assembly process, when welding and joining two metals together, the zinc coating is burned off and destroyed, making the metal extremely susceptible to the rusting process. The zinc layer acts as a galvanic anode rusting in preference.
Galvanization consists of coating metal with a thin layer of another such metal, which often fails at seams, holes and joints where the coating is pierced.
