Corrosion as an Electrochemical Process

Corrosion is the conversion of metals into their oxide as a result of contact with moisture and air. The corrosion of iron is known as rusting. 

Iron rusts when it comes into contact with air and water because electrochemical cells are set up at the surface of contact.

At the anodeAn anode is an electrode of a polarized electrical device through which conventional current enters the device. It is the positive part of electrolytes where oxidation takes place. More (Anodic region)

Metallic iron is oxidized to give Iron(II) ions 

Fe_(s) →  Fe²⁺_(aq) + 2e^–

At the cathodeA cathode is the electrode from which a conventional current leaves the electrolyte. It is the negative part of the cell where reduction takes place. More (Cathodic Region)