Question

4. Precipitation Hardening of Al-Cu: Aluminum-rich aluminum-copper alloys are precipitation hardenable. The precipitation hardening process consists of two heat treatment steps: (1) a solution heat treatment, during which all solute atoms are dissolved to form a single-phase $alpha$ solid solution, followed by quenching to RT and (2) a precipitation heat treatment, during which the supersaturated $alpha$ solid solution is heated to and held at an intermediate temperature within the 2-phase region, followed by cooling to RT (20 points) (a) First, we must choose the composition range that is available for precipitation hardening. Label the available range in the phase diagram and explain your choice (b) Suppose we begin with a Al-Cu alloy, with 5 wt% Cu at RT. What range of temperatures would enable us to solution heat treat the alloy? Label the appropriate temperature range in the phase diagram and explain your choice (c) For the precipitation heat treatment, we heat our sample to 400°C in order to nucleate $CuAl_2$ particles within the $alpha$ matrix. What are the compositions of the $CuAl_2$ particles and $alpha$ matrix, respectively? [Hint: you may wish to draw a tie-line] (d) Compute the weight fractions of $CuAl_2$ and $alpha$ phases [Hint: use the Lever Rule]

          4. Precipitation Hardening of Al-Cu: Aluminum-rich aluminum-copper alloys
are precipitation hardenable. The precipitation hardening process consists of two
heat treatment steps: (1) a solution heat treatment, during which all solute atoms
are dissolved to form
a single-phase $alpha$ solid
solution, followed by
quenching to RT and
(2) a precipitation
heat treatment,
during which the
supersaturated $alpha$
solid solution is
heated to and held at
an intermediate
temperature within
the 2-phase region,
followed by cooling
to RT (20 points)
(a) First, we must choose the composition range that is available for precipitation
hardening. Label the available range in the phase diagram and explain your choice
(b) Suppose we begin with a Al-Cu alloy, with 5 wt% Cu at RT. What range of
temperatures would enable us to solution heat treat the alloy? Label the appropriate
temperature range in the phase diagram and explain your choice
(c) For the precipitation heat treatment, we heat our sample to 400°C in order to
nucleate $CuAl_2$ particles within the $alpha$ matrix. What are the compositions of the
$CuAl_2$ particles and $alpha$ matrix, respectively? [Hint: you may wish to draw a tie-line]
(d) Compute the weight fractions of $CuAl_2$ and $alpha$ phases [Hint: use the Lever Rule]

$4. Precipitation Hardening of Al-Cu: Aluminum-rich aluminum-copper alloys are precipitation hardenable. The precipitation hardening process consists of two heat treatment steps: (1) a solution heat treatment, during which all solute atoms are dissolved to form a single-phase alpha solid solution, followed by quenching to RT and (2) a precipitation heat treatment, during which the supersaturated alpha solid solution is heated to and held at an intermediate temperature within the 2-phase region, followed by cooling to RT (20 points) (a) First, we must choose the composition range that is available for precipitation hardening. Label the available range in the phase diagram and explain your choice (b) Suppose we begin with a Al-Cu alloy, with 5 wt% Cu at RT. What range of temperatures would enable us to solution heat treat the alloy? Label the appropriate temperature range in the phase diagram and explain your choice (c) For the precipitation heat treatment, we heat our sample to 400°C in order to nucleate CuAl2 particles within the alpha matrix. What are the compositions of the CuAl2 particles and alpha matrix, respectively? [Hint: you may wish to draw a tie-line] (d) Compute the weight fractions of CuAl2 and alpha phases [Hint: use the Lever Rule]$

Added by Edward R.

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