Metals crystallize but owing to their other characteristics the crystals are rarely discussed. Some metals such as gold are too soft to use if not alloyed.
Alloying can deal with substitution of specific metal atoms into the matrix so one might achieve the same strength with a lighter density.
Some alloys are made to resist wear by achieving hardness--Read more about (Rockwell Hardness). or precious metal as such as gold and alloys of 12, 14, 18 and 24 karat.
Other alloys provide for a more uniform expansion or resistance to expansion. or resistance to corrosion, such as brass or a controlled corrosion such as the patina of bronze