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 400ºC 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, eF, significantly increased with increasing the number of ECAP passes up to 8 at 130ºC. The alloy processed under these conditions exhibited a maximum value of 322% at 300ºC and an initial strain rate of 10−3 s−1. High strain rate superplasticity was obtained at this temperature, eF=210%, at 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 above temperatures of 350ºC is related to abnormal grain growth and a change of deformation mechanism.