The Bronzes

The coinage bronze used for making coins in earlier days contains 95% Cu, 4% Sn and 1 % Zn. The Zn acts as a deoxidiser. This alloy is soft and ductile.

Admiralty gun metal contains 88% Cu, 10% Sn and 2% Zn. This bronze is normally cast to produce steam and water fittings and bearings. The addition of Pb improves the pressure tightness of the alloy.

Phosphor bronzes are commonly used in manufacture of bearings, hard drawn wires and bronze springs. In addition to tin they contain small percentage of phosphorous as alloying element. 0.2% P forms Cu3P which is a hard compound. It acts as deoxidiser and improves fluidity.

Copper aluminium alloys posses high strength with good resistance to fatigue, corrosion and abrasion and are golden in colour. Aluminium can dissolve in copper to the extent of 9% and greater content than this induces brittleness. Wrought alloys which are good for hot and cold working applications contain 5 to 7% Al. Casting alloys contain 10% Al. Small percentage of Fe, Ni and Mn are added to casting alloys to make them more easily heat treatable. Aluminium bronze is well known for its colour and often called Imitation gold. Al bronze compares well with the strength of steel.

Bronzes in general are known for the following characteristics :
a.    costlier than brass,
b.    better corrosion resistance,
c.    stronger than brass, and
d.    bearing material.