Question

Please show me how they get answer d)

Question B1. Atomic percent magnesium 10 20 30 40 50 60 70 80 90 700 649 1200 1100 -1000 500 900 451 -800 598 67.7 14.9 87.3 400 700 600 500 400 200 100 AI 10 20 30 40 50 60 70 80 90 Mg Weight percent magnesium Figure 1: Aluminium-Magnesium equilibrium phase diagram. (Source: Metals Handbook, 8th Edition. Vol 8 American Society for Metals p. 261.) Consider an Al-7 wt% Mg alloy (phase diagram above). Which of the following is the best description of the equilibrium microstructure of this alloy at room temperature (assume that the solubility of Mg in Al does not change from that shown at 100°C)? a) A eutectic mixture containing 18 wt% β phase and 82 wt% α phase. b) Dendrites of α phase surrounded by a eutectic containing 1 wt% α phase and 34 wt% ß phase. c) Small amounts of ferrite in a matrix of the β phase. d) Approximately 18 wt% β phase in the grain boundaries of the α phase. e) Approximately 18 wt% of fine α phase precipitates inside the grains of the β phase.

Answer 1

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