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HW10 ENME382 S10 Section0201 solution

# HW10 ENME382 S10 Section0201 solution - ENME 382 Section...

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ENME 382 Section 0201 Homework 10 Due in class: May 7, 2010 1 Cite the phases that are present and the phase compositions for the following alloys: (a) 25 wt% Pb–75 wt% Mg at 425°C (800°F) (b) 55 wt% Zn–45 wt% Cu at 600°C (1110°F) (c) 7.6 lb m Cu and 144.4 lb m Zn at 600°C (1110°F) (d) 4.2 mol Cu and 1.1 mol Ag at 900°C (1650°F) Solution (a) For an alloy composed of 25 wt% Pb-75 wt% Mg and at 425 ° C, from Figure 10.20, only the α phase is present; its composition is 25 wt% Pb-75 wt% Mg. (b) For an alloy composed of 55 wt% Zn-45 wt% Cu and at 600 ° C, from Figure 10.19, β and γ phases are present, and C β = 51 wt% Zn-49 wt% Cu C γ = 58 wt% Zn-42 wt% Cu (c) For an alloy composed of 7.6 lb m Cu and 144.4 lb m Zn and at 600 ° C, we must first determine the Cu and Zn concentrations (using Equation 5.6), as C Cu = 7.6 lb m 7.6 lb m + 144.4 lb m × 100 = 5.0 wt% C Zn = 144.4 lb m 7.6 lb m + 144.4 lb m × 100 = 95.0 wt% From Figure 10.19, only the L phase is present; its composition is 95.0 wt% Zn-5.0 wt% Cu (d) For an alloy composed of 4.2 mol Cu and 1.1 mol Ag and at 900 ° C, it is necessary to determine the Cu and Ag concentrations in weight percent. However, we must first compute the masses of Cu and Ag (in grams) using a rearranged form of Equation 5.7: m Cu ' = n m Cu A Cu = (4.2 mol)(63.55 g/mol) = 266.9 g m Ag ' = n m Ag A Ag = (1.1 mol)(107.87 g/mol) = 118.7 g

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Now, using Equation 5.6, concentrations of Cu and Ag are determined as follows: C Cu = 266.9 g 266.9 g + 118.7 g × 100 = 69.2 wt% C Ag = 118.7 g 266.9 g + 118.7 g × 100 = 30.8 wt% From Figure 10.7, α and liquid phases are present; and C α = 8 wt% Ag-92 w% Cu C L = 45 wt% Ag-55 wt% Cu 2 A 50 wt% Ni–50 wt% Cu alloy is slowly cooled from 1400°C (2550°F) to 1200°C (2190°F).
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