Re: why do people make alloys?

Well, without alloys, there would only be pure metals.  There really are 
not very many of them in common use:  Gold, Silver, Iron, copper.  When a 
material is needed to do something which these metals cannot do, alloys are 
used.  If we want something to hold water, Iron would rust, and the copper 
would form a toxic oxide.  Gold or silver would be expensive, so the steel 
is alloyed with carbon, nickel and chromium to make stainless steel.

Other properties besides corrosoin resistance might be ductility, 
wear resistance, strength, hardness, electrical properties, such as 
conductivity, thermal properties, such as heat transfer or 
expansion/contraction, etc.  The reason there are so many alloys is that 
there are so many possible requirements on a material.