Corrosion is a natural process of wasting of the metal due to the reaction of the metal with environmental factors like moisture, oxygen etc to form corresponding hydroxides, oxides on the surface of the metal.

Corrosion contributes to the major loss of metal in terms of its quality and usefulness with time. Corrosion generally degrades the base metal in terms of important properties like strength, appearance and permeability to liquids and gases. Corrosion in some cases can be useful as it protects the base metal from further reaction eg corrosion in case aluminium as it forms aluminium oxide and protects the base metal.