Aluminum is a silvery white metal, ranking third only after oxygen and silicon in the crust. The density of aluminum is small, only 34.61% of iron and 30.33% of copper, so it is also called light metal. Aluminum is a nonferrous metal whose output and consumption are second only to steel in the world. The density of aluminum is only 2.7103g/cm ³， About 1/3 of the density of steel, copper or brass. Due to its light material, aluminum is often used to manufacture land, sea and air transportation vehicles such as automobiles, trains, subways, ships, aircraft, rockets and airships to reduce self weight and increase loading capacity.