The purposes of making an alloy with example:
1. Improve hardness of metal e.g. Pure gold & silver are soft. Hence they are hardened by the addition of a small amount of copper in them.
2. Lower the melting point e.g. Wood’s metal is an alloy of Bi, Pb, Sn, Cd. It has the M.P. 710C which is much lower than those of its constituents.
3. Increase the tensile strength e.g. The addition of 1% carbon increase the tensile strength of pure iron by about 10 times.
4. Increase corrosion resistance e.g. Pure iron is corroded fastly but its alloy stainless steel resist corrosion.
5. To get good casting e.g. Bronze (an alloy of Cu & Zn) and Duralumin possess good casting property.
6. Modify colour e.g. Brass is an alloy of copper (red) and zinc (silvery white) and is yellow in colour.
7. Reduce malleability & ductility e.g. a small amount of copper is added to gold and silver to reduce their malleability and ductility.
8. Modify chemical activity e.g. Sodium is highly reactive element, but when it is alloyed with mercury to form an alloy called sodium- amalgam , it becomes less reactive.