Effect of high-pressure torsion on grain refinement, strength enhancement and uniform ductility of EZ magnesium alloy

Strength enhancement of Mg-based alloys without deteriorating their ductility is currently a major scientific and industrial challenge. In this study, discs of as-cast EZ33A alloy were processed by high-pressure torsion (HPT). The coarse-grained cast material was turned to ultrafine-grained (UFG) of ∼240 nm, ∼135 nm and ∼127 nm size, after 1, 3 and 10 turns, respectively. Simultaneously, hardness increased from 60 HV for the as-cast material to 90-95 HV after HPT processing. Samples subjected to various HPT routes showed enhanced ultimate tensile strength of 270 MPa, along with their uniform elongation up to 10%. The simultaneous increase of strength and ductility was attributed to the bimodal grain size distribution, as well as to the fragmentation and redistribution of brittle (Mg,Zn)12Ce phase.