A 50 wt% Pb-50 wt% Mg alloy is slowly cooled from 700C (1290F) to 400C (750F). (a) At what temperature does the first solid phase form? (b) What is the composition of this solid phase? (c) At what temperature does the liquid solidify? (d) What is the composition of this last remaining liquid phase?

Explanation:

a)  the temperature at which the  first solid phase  form is calculated upon the cooling from 700°c , the first solid phase form at the temperature at which a vertical line at their composition intersect the line L - ( ∝ + L) Phase boundary i.e about 360°c.

b) What is the composition of this solid phase?  ; the composition of the first solid phase form corresponds to the intersection with the ∝ - (∝+L) phase boundary at a line constructed across the  (∝+L) phase.  Region at 560°c i.e 21wty. Pb or -79wty.mg

c) temperature at which the liquid completely solidify is about 465°C which is obtained by the intersection of the composition. wt; pbg so with the eutectic isotherm , i.e about 465°c.

d) the composition of the last remaining liquid face prior to the complete solidification corresponds to the eutectic composition. i.e 67wty.Pb - 33wty. mg