Give the purposes of making of an alloy.

Alloys are made in order to:

1. Increase hardness and strength. Pure metals are soft. Example: adding C to Fe gives steel; adding Cu to Au makes gold hard enough for jewellery.
2. Lower the melting point. Example: solder (Pb–Sn) and Wood's metal melt at low temperatures.
3. Improve corrosion resistance. Example: stainless steel (Fe–Cr–Ni); bronze resists corrosion better than Cu.
4. Improve castability. Alloys expand on solidifying, which gives sharp castings. Example: type metal (Pb–Sb–Sn).
5. Change the colour. Example: brass (Cu–Zn) is golden yellow; aluminium bronze looks like gold.
6. Modify electrical and magnetic properties. Example: nichrome has high resistance for heating elements; alnico is used for magnets.
7. Improve machinability and resistance to wear.