Metal corrosion is essentially an electrochemical reaction. Oxidation occurs at the anode and reduction occurs at the cathode due to ionic current through an electrolyte, usually water, &electron current through the metal. Other elements or contaminants present may act as catalysts. Major factors affecting corrosion of metals are - metallurgy (electro-potential, surface roughness), fluctuations in humidity & temperature, and residues (contaminants) on the metal surface.
