Aluminum, after iron is the second -most widespread metal used on earth. Unpainted aluminum forms a protective aluminum oxide layer over the pure aluminum metal alloy and, in most atmospheric environments, is resistant to corrosion deterioration. However, pure aluminum is virtually always alloyed with other metallic elements to enhance its properties, primarily to increase its strength, but also to improve its formability, weldability, machineability, electrical conductivity, and corrosion resistance.