Figure Q1 below shows the equilibrium phase diagram of Lead (Pb)-Tin (Sn) alloy system. (a) (b) (c) Temperature (C) (ii) 300 200 100 327C a+L 18.3 20 183C 40 *** Liquid 61.9 60 (Pb) Composition (wt% Sn) (Sn) Figure Q1 The equilibrium phase diagram of Lead (Pb)-Tin (Sn) alloy system At a temperature of 200 C, a melt of 20 wt% Pb-80wt% Sn alloy with a mass of 100 g should have two phases, i.e., solid and liquid L phases, respectively. Without changing the temperature of this alloy, please (i) 80 232 C 97.8 100 Suggest how to make this melt become a completely solid phase by changing the composition. Suggest how to make this melt become a completely liquid phase by changing the composition. Suggest one method to strengthen the 20 wt% Pb-80wt% Sn alloy with detailed explanation and justification. Based on the Pb-Sn alloy phase diagram, explain why Pb-Sn alloy was widely used as the solder material in the reflow soldering process in the past and it is much less used in the electronic packaging nowadays.