What is an alloy called when it melts at the same temperature as something else?
Isotectic substances are those which melt at the same temperature. 


Ref.: Heycock, C. T.; Neville, F. H. "On the freezing points of triple alloys of gold, cadmium, and tin". J. Chem. Soc., Trans., 1891, 59, 936-966

But be aware that this term is very rarely used.