Answer:
hello your question is incomplete attached below is the complete question
answer : 550°c
Step-by-step explanation:
From the phase diagram attached we can see that at point between 500° and 600° i.e.550°c on the phase diagram the first solid phase was form when a 55 wt% Pb-45 wt% Mg alloy slowly cools down from 700 to 300°c