High strain rate superplasticity at intermediate temperatures of the Al 7075 alloy severely processed by equal channel angular pressing

Abstract

The mechanical properties of an overaged Al 7075-O alloy processed by ECAP were examined by tensile tests at intermediate-high temperatures ranging from 250 to 400 °C and strain rates from 10 −5 to 10 −1 s −1. The influence of the number of ECAP passes on the ductility enhancement was evaluated. Elongation to failure, e F, significantly increased with increasing the number of ECAP passes up to 8 at 130 °C. The alloy processed under these conditions exhibited a maximum value of 322% at 300 °C and an initial strain rate of 10 −3 s −1. High strain rate, e F = 210%, at a strain rate as high as 10 −2 s −1. The large elongations together with lower stresses and lower stress exponents than those for the start material confirm that grain boundary sliding (GBS) is the operative deformation mechanism. A loss of superplastic behaviour at temperatures above 350 °C is related to abnormal grain growth and a change of deformation mechanism.