Herein, the ultrafine-grained (UFG) 7xxx series alloy Al–4.8Zn–1.2Mg–0.14Zr
demonstrates superplasticity at unusually low temperatures of 120–170 C while
maintaining its high-strength state. The UFG structure is formed by high
pressure torsion (HPT) at room temperature (RT), which leads to a considerable
increase in the strength characteristics by ~60% compared with the material
after conventional heat treatment T6. It is found that the UFG alloy exhibits
thermostability when testing or annealing up to 170 C. Deforming by tensile test
at a strain rate of 10-4 s-1 and 10-3 s-1, the elongation to failure at 120 and
170 C exceeds 250% and 500%, respectively, whereas the strain rate sensitivity
reaches 0.45, which is a typical value characterizing superplastic deformation.
After superplastic deformation, the UFG alloy maintains 25–50% higher strength
characteristics at RT than that after conventional heat treatment T6. The origin of
such superior behavior of the UFG alloy is discussed.