Cyclic softening of ultrafine-grained AZ31 magnesium alloy processed by equal-channel angular pressing

The low-cycle tension–compression fatigue tests were performed at ambient temperature on ultrafine grained AZ31 magnesium alloy processed by equal channel angular pressing. All samples exhibited cyclic softening, and the softening effect increased with increasing total strain amplitude. Observations by optical microscope revealed that pronounced recrystallization occurred, and the direction of larger axis of recrystallized grains was nearly 45° with respect to the loading axis. Local grain coarsening leads to the formation of dense shear localization, while line-like damage traces remain in fine grains. A model is proposed to account for the recrystallization, based on the characteristic distribution of defects introduced by equal channel angular pressing.

► ECAPed AZ31 exhibits cyclic softening during low-cycle fatigue.
► The larger axis of recrystallized grains was parallel to the shear plane of ECAP.
► Two kinds of shear bands appeared, dense shear bands and line-like traces.
► Recrystallization is related to the local microstructure inhomogeneity.