Strain rate effect on the cyclic deformation response of UFG Al alloys

Abstract

► We studied the cyclic deformation response of UFG Al to strain rate change. ► The materials considered for this study were commercially pure Al and 2024 Al alloy. ► The cyclic softening rate in UFG pure Al was not strain rate sensitive. ► However, the appearance of shear bands was found strain rate sensitive. ► The stable behaviour of UFG 2024 Al alloy was also found insensitive to strain rate. Commercially pure aluminium and 2024 Al alloy were cryo-rolled and annealed to produce ultrafine grained (UFG) microstructures. Both materials were cyclically deformed under a fully reversed total strain amplitude control condition at different frequencies to study strain rate effects. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to identify microstructural changes and explain the mechanical properties. The cyclic stress response showed significant softening in commercial purity Al that was due to shear band formation and grain coarsening within these shear bands. While there was no strain rate sensitivity for commercial purity Al in terms of the mechanical response, the shear bands became noticeably more defined at lower strain rates. 2024 Al alloy had a cyclically stable response and microstructure that was not affected by strain rate.