Al copper alloys

Question 1

precipitation strengthing (hardening) of Al Cu alloys is done by

Answer 1

solution treatment at 515 degrees to dissolve all copper
quenched in water to room temp all of the solute copper is trapped
then artificially aged at temp between 130 and 190

Question 2

during solution treatment what happens to both Al and Cu atoms

Answer 2

they diffuse randomly into a uniform substitutional solid solution( alpha phase on diagram)

Question 3

in qunching of Al and
Cu what is produced

Answer 3

supersaturated solid solution of copper in aluminium.

Question 4

for Al-Cu alloy in ssss condition is it stable?

Answer 4

its not stable and strives to form more stable (meta stable) to lower the overall energy of the system

Question 5

what structures are formed from aging of Al-Cu alloys

Answer 5

ssss( as quenched)
GP1 zones
GP 2 zonea
theta dash phase
theta phase(EQ) stable
gp zones are meta stable

Question 6

gp1 zone information

Answer 6

GP 1 zones are formed homogeneously at low temperatures (ie. 130 oC or below).
* They consist of disks a few copper atoms thick (4 – 6 A) and about 80 – 100
A in diameter.
* Cu atoms are about 11% smaller in diameter than Al atoms. Their lattice
parameter is less than that of the matrix and hence a strain field is formed,
though they remain coherent with the matrix.
* The zones, and their associated strain field inhibit dislocation movement and
increase the strength and decrease the ductility of the alloy

Question 7

gp zone 2

Answer 7

form homogeneously at around 130 oC after quite long ageing
times.
* They are about 10 – 40 A thick and around 100 – 1000 A in diameter and are
also coherent. They produce a further increase in strength.