Improvement of mechanical characteristics in severely plastic-deformed Mg alloys

The commercial pure Mg, AZ31 and AZ61 alloys were severly plastic-deformed through equal channel angular pressing (ECAP). The grain size of pure Mg was decreased from 400 to 80 mum after ECAP and the 4 ECA pressed AZ31 alloy revealed the mixed microstructure of fine grains of less than 5 mum and coarser grains of approximately 5 similar to 10 mum. Newly formed grains were attributed to dynamic recrystallization during ECAP at temperatures of higher than 1/2 T-m, where T-m is melting temperature. There was small increase of microhardness, yield stress and tensile strength in the ECA pressed pure Mg, while those of AZ31 and AZ61 alloys drastically increased after I pressing. The yield stress in the ECA pressed AZ31 and AZ61 alloys gradually decreased with increasing the number of pressings, but the tensile strength increased slightly. In particular, there was a typical tensile characteristic when compared with the other ECA pressed metals; a marked improvement in elongation was found concurrent with the pronounced strain hardening, without sacrificing the tensile strength, in the 4 ECA pressed AZ31 and AZ61 alloys. These tensile deformation characteristics were explained based on the observation of the deformed microstructure in the vicinity of fracture surface.