Question

Advantages & disadvantages of metal alloys?

Answer 1

that is a really wide field. almost all metals you meet in daily live are alloys.
pure metal is in most cases to soft for use or corrodes pretty fast. so to get a metal that is harder you add some other materials in your melting, like carbon is added to iron to get steel.
some additions can also lower the melting point than it would be for each of the components, some additions provide better electric conductivity, and so on. the list of advantages is long.

disadvantage might be in case for recycling that you have a mixture of a lot of different elements instead for just one metal.