Microstructure evolution of heavily deformed AA5083 Al-Mg alloy studied by positron annihilation spectroscopy

Commercial Al-Mg alloy AA5083 was severely deformed with thickness reduction from 50 mm to 1 mm by hot rolling plus cold rolling. Isochronal annealing studies of this heavily deformed Al-Mg alloy were investigated by positron annihilation and Vickers microhardness as well as X-ray diffraction measurements. Positrons are almost fully trapped at dislocations in the as deformed sample. This suggests that deformation introduces large amounts of dislocations. The Vickers microhardness also increases from 71 Hv to 155 Hv after deformation. Most of the deformation induced dislocations are annealed out at 250 °C. At the same time, the microhardness also decreases to about 90 Hv after annealing at 200-250 °C and remain stable after further annealing up to 500 °C. This indicates that hardening of the AA5083 alloy is primarily due to dislocations. Dislocation-solute interaction may be also responsible for the strengthening of hardness.