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Name: HW#8, 9&10 of ETM307: Materials Science 70 pts in total and due on July 25, 2018, Wednesday 1. Please describe the microstructural changes in the three stages of recovery, recrystallization and grain growth during annealing treatment. (20 pts) 2. Please explain why micro-segregation and macro-segregation happen during practical solidification. (10 pts) For materials science, the essential point is to figure out an effective way to increase materials strength without significantly compromising ductility. When we leamed precipitation strengthening, we knew that, for a given amount of an alloying element, fine and uniform-distributed precipitates generated by the alloying element are more efficient in increasing materials strength than the element's atoms staying as solid solution atoms. We just finished learning the aging treatment of Al alloys, the questions for you are: 3. You are given an equilibrium-solidified Al-Cu alloy indicated in Figure 1. Please advise a heat treatment procedure that can be used to achieve a maximum strength without losing a significant amount of ductility. Please draw your temperature history in the temperature-time coordinate beside the phase diagram and describe the microstructure change in each heat treatment step. (40 pts) 800 CuAl2(0) L 1 600 La αι 548°C Temperature (°C) 400 Temperature (°C) a +0 200 0 0 10 50 60 Time Fig. 1 20 30 40 Copper (wt.%)
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1 Please describe the microstructural changes in the three stage of recovery, recrystallization and
grain growth during annealing process.
Answer
Annealing- is a heat treatment process that alters the physical and at times the chemical
properties of a material thus increasing its ductility and inversely reducing its hardness. The three
stages of the annealing process, proceeding with increasing temperature are; recovery stage,
recrystallization stageand grain growth.
Recovery-This is the first stage. It occurs at lower temperatures of all the other two processes. It
involves removal of linear defects, dislocations, and the internal stresses. The grain size and
shape do not change.
Recrystallization- This is the second stage. At this stage the grains that were deformed are
replaced by distinct new defect free grains that nucleate and grow, forming a new microstructure.
It involves short range diffusion. It is time dependent, the longer the time the higher the
recrystallization.
Grain growth- This is the third stage. After recrystallization the strain free grains will continue to
grow in grain size in the material at elevated temperature. The microstructure therefore
coarsens.As the grains increase in size, total boundary area reduces, yielding a decrease in the
t...


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