Low-Temperature and high-Strain-Rate superplasticity of ultrafine-Grained A7075 processed by high-Pressure torsion

Abstract

An A7075 alloy was processed by high-pressure torsion (HPT) under an applied pressure of 6 GPa for 1, 3 and 5 revolutions with a rotation speed of 1 rpm at room temperature. Vickers microhardness saturated to a level of 220 Hv after the HPT processing and the grain size was refined to 3120 nm at the state of the hardness saturation. Tensile tests were conducted with initial strain rates from 2.0 © 1012 to 2.0 © 1014 s11 at a temperature in the range of 200400°C. It was shown that high-strain rate superplasticity (>1.0 © 1012 s11) and/or low-temperature superplasticity (0.50.6Tm) occurred in the HPT-processed A7075 alloy, where the superplasticity deformation is controlled by grain boundary sliding through grain boundary diffusion.