Metals are always alloyed to change one, or a range, of their physical properties. This may be to improve the strength an corrosion resistance of aluminium to make it possible to use in the construction, automotive and aircraft industries. In the steel industry metals like chromium are added to make "stainless steel" tungsten is mixed to create hard industrial tool steels. Super powerful magnets are iron based with niobium as the additive.
Pure gold is too soft to be used for most purposes so silver is added and to get rose gold copper is mixed during the smelting process. One of the most ancient alloys was bronze "The Bronze Age in Ancient History" which is copper and tin which made the copper much harder so tools did not bend as much and could keep sharp longer.
I hope this gets you out of your homework problem a little.