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Chapter 9: Problem 42

For a 64 wt \% Zn-36 wt\% Cu alloy, make schematic sketches of the microstructure that would be observed for conditions of very slow cooling at the following temperatures: \(900^{\circ} \mathrm{C}\left(1650^{\circ} \mathrm{F}\right), 820^{\circ} \mathrm{C}\) \(\left(1510^{\circ} \mathrm{F}\right), 750^{\circ} \mathrm{C}\left(1380^{\circ} \mathrm{F}\right)\), and \(600^{\circ} \mathrm{C}\left(1100^{\circ} \mathrm{F}\right)\) Label all phases and indicate their approximate compositions.

Short Answer

Expert verified
Question: Describe the microstructure of a 64 wt% Zn-36 wt% Cu alloy during slow cooling at 900°C, 820°C, 750°C, and 600°C using the Zn-Cu phase diagram. Answer: During slow cooling of a 64 wt% Zn-36 wt% Cu alloy, at 900°C the alloy is in the Liquid phase. At 820°C, there are two phases present: Liquid phase and α phase (approx. 53 wt% Zn). At 750°C, the alloy consists of only the α phase with the same 64 wt% Zn-36 wt% Cu composition as the original alloy. Finally, at 600°C, the microstructure contains both α phase (approx. 19 wt% Cu) and β phase (approx. 73 wt% Cu).

Step by step solution

01

Interpret the Zn-Cu phase diagram at 900°C

At 900°C, the Zn-Cu phase diagram indicates that the 64 wt% Zn-36 wt% Cu alloy is in the Liquid phase.
02

Sketch the microstructure at 900°C

Since the alloy is in the Liquid phase at this temperature, there is no solid microstructure yet. The schematic sketch will show a homogeneous liquid.
03

Interpret the Zn-Cu phase diagram at 820°C

At 820°C, the Zn-Cu phase diagram indicates the presence of two phases: Liquid phase and α phase, with the α phase having approximately 53 wt% Zn.
04

Sketch the microstructure at 820°C

The schematic sketch for the 820°C microstructure should show the presence of both Liquid and α phase regions, with α-phase regions having a composition of around 53 wt% Zn.
05

Interpret the Zn-Cu phase diagram at 750°C

At 750°C, the Zn-Cu phase diagram indicates the presence of only the α phase with the same 64 wt% Zn-36 wt% Cu composition as the original alloy.
06

Sketch the microstructure at 750°C

The schematic sketch for the 750°C microstructure should show only the α phase with a composition of the alloy that is 64 wt % Zn. This sketch would represent a homogeneous solid solution.
07

Interpret the Zn-Cu phase diagram at 600°C

At 600°C, the Zn-Cu phase diagram indicates the presence of two phases: α phase and β phase, with the α phase having approximately 19 wt% Cu and the β phase having approximately 73 wt% Cu.
08

Sketch the microstructure at 600°C

The schematic sketch for the 600°C microstructure should show the presence of both α and β phase regions, with α-phase rich regions having a composition of around 19 wt% Cu and β-phase rich regions having a composition of around 73 wt% Cu.

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Most popular questions from this chapter

The mass fractions of total ferrite and total cementite in an iron-carbon alloy are \(0.91\) and \(0.09\), respectively. Is this a hypoeutectoid or hypereutectoid alloy? Why?

Consider \(1.5 \mathrm{~kg}\) of a \(99.7 \mathrm{wt} \% \mathrm{Fe}-0.3 \mathrm{wt} \%\) C alloy that is cooled to a temperature just below the eutectoid. (a) How many kilograms of proeutectoid ferrite form? (b) How many kilograms of eutectoid ferrite form? (c) How many kilograms of cementite form?

Consider \(6.0 \mathrm{~kg}\) of austenite containing \(0.45 \mathrm{wt} \%\) \(\mathrm{C}\) and cooled to less than \(727^{\circ} \mathrm{C}\left(1341^{\circ} \mathrm{F}\right)\). (a) What is the proeutectoid phase? (b) How many kilograms each of total ferrite and cementite form? (c) How many kilograms each of pearlite and the proeutectoid phase form? (d) Schematically sketch and label the resulting microstructure.

For \(5.7 \mathrm{~kg}\) of a magnesium-lead alloy of composition \(50 \mathrm{wt} \% \mathrm{~Pb}-50 \mathrm{wt} \% \mathrm{Mg}\), is it possible, at equilibrium, to have \(\alpha\) and \(\mathrm{Mg}_{2} \mathrm{~Pb}\) phases with respective masses of \(5.13\) and \(0.57 \mathrm{~kg} ?\) If so, what will be the approximate temperature of the alloy? If such an alloy is not possible, then explain why.

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