The fuse wire is made up of lead and tin alloy as this alloy has a very low melting point and a very high resistivity. When a large amount of current flows through this alloy, due to the high resistivity heat is produced due to the flow of high current Which make the alloy melts (as it has a very low melting point). Thus,as alloy melts the circuit breaks and the appliances connected to it are saved from any damage due to the high amount of current flowing in the circuit.