"To craft powerful items"
Alloys are an important material for making powerful weapons and bots. They can be crafted using a Smelter, you need 1 Iron + 1 Junk + 1 Sulfur.
You can also collect alloys by killing armored ghoul, but it's better not to do it, unless they are attacking you anyway. More advanced players often kill armored ghouls for alloys, and craft a sulfur pickaxe very early game.
Alloys are used in the crafting recipe of all the bots and guns, excluding 9mm. It is also used in crafting the sulfur axe, though the sulfur axe is more easily and commonly obtained at resetting at level 25.
Also you can found alloys in the bunker, but is VERY rare