Aluminum is a silvery white metal, which ranks third in the earth's crust after oxygen and silicon. 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 non-ferrous metal whose output and consumption are second only to steel in the world. The density of aluminum is only 2.7103g/cm3, about 1 / 3 of that of steel, copper or brass. Due to the light material of aluminum, it is often used to manufacture land, sea and air vehicles such as cars, trains, subways, ships, aircraft, rockets and spaceships, so as to reduce the self weight and increase the loading capacity.