A lead (40%) tin alloy that is cooled from 300 degrees C to room temperature starts as a liquid and ends as a solid.

Describe the stages and composition of the grains, as follows:

• Using the Sn-PB phase diagram in the textbook, calculate the initial and final temperatures where the mixture solidifies.
• Using the lever rule, calculate the initial composition of the alpha and beta phases for the solidifying metal.
• Would the resulting grains size be smaller or larger if cooled fast or slowly?

Composition = 0 at% Sn Composition = 0 wt% Sn Temperature = 0 C Temperature = 32 F = Composition (at% Sn) 60 0 20 40 80 100 327 C 600 300 Liquid 500 Liquid al 232 C 200 400 a 183 C B+L Temperature (C) 18.3 61.9 97.8 Temperature (F) 300 100! a +B 200 100 0 20 80 100 40 60 Composition (wt% Sn) (Pb) (Sn)