What alloy does tin make when mixed with copper?
Both tin and copper as the pure metals are relatively soft, and do not hold an edge. When the metals are mixed as an alloy, approx. 10-12% tin, the alloy bronze is made. This alloy is hard, and edged tools made from this material hold an excellent edge....and such bronze tools are resistant to corrosion...so much so that statues cast from bronze have been retrieved in good nick from the sea after over 2000 years..
See this answer for more examples of alloys.