Corrosion, a chemical process in which metal is slowly broken down and eaten away. The most common form of corrosion is caused by oxidation (the combining of oxygen with the metal). Corrosion can also result from the chemical combination of a metal with gases other than oxygen, with acids, or with salts. The process is prevented by painting or by coating or plating the metal with zinc, nickel, tin, chromium, or other corrosion-resistant substances. Another way is to alloy the metal with noncorroding metal.