Exceptional mechanical properties of ultra-fine grain AZ31 alloy by the combined processing of ECAP, rolling and EPT

AZ31 Mg alloy with homogeneous refined microstructure and excellent mechanical properties was obtained in this paper by the combined technology of equal-channel angular pressing (ECAP), rolling and electropulsing treatment (EPT). Compared to those of the as-received samples, the average grain size of the EPTed samples is refined from 22 mu m to 1.2 mu m, accordingly the yields stress (YS) and ultimate tensile strength (UTS) are increased from 205 MPa and MPa to 320 MPa and 430 MPa, respectively. The recrystallization of EPTed samples during different stages indicates that the recrystallization of the deformed Mg alloy is mainly affected by the processing time and duration of EPT. Based on the measured temperature of samples processed by EPT, a furnace annealing control-experiment was conducted on the deformed samples, and the recrystallization of the rolled metal did not occur at the given annealing temperature. It is revealed by theory and experiment analysis that EPT works through its athermal effect as well as thermal effect, which increase the Gibbs free energy and the additional atomic diffusion flux and in result accelerate the recrystallization of the deformed AZ31 alloy at lower temperature.