Aluminium is a chemical element; it has symbol Al and atomic number 13. Aluminium has a density lower than that of other common metals, about one-third that of steel. 

Steel is an alloy of iron and carbon with improved strength and fracture resistance compared to other forms of iron. Because of its high tensile strength and low cost, steel is one of the most commonly manufactured materials in the world.

Brass is an alloy of copper and zinc, in proportions which can be varied to achieve different colors and mechanical, electrical, acoustic, and chemical properties, but copper typically has the larger proportion.

Copper is a chemical element; it has symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. 

A nickel alloy is a metal that contains a percentage of nickel in its elemental makeup. Nickel is primarily alloyed with chromium, copper, iron, titanium, and molybdenum. Each of these alloy combinations has specific properties that make it best suited to a certain range of applications.