Structure homogeneity and low-temperature micromecanical properties of ultrafine-grained magnesium alloy AZ31

The degree of microstructure homogeneity for an ultrafine-grained (UFG) AZ31 magnesium alloy obtained by special thermomechanical treatment including four passes of equal-channel angular pressing (ECAP, Route Bc) was studied by the microindentation method. The defect structure of the UFG alloy was found to be reasonably homogeneous. The texture associated with ECAP results in lower values of microhardness measured on the plane normal to the extrusion axis as compared to those on a plane containing the axis, and also in some dependence of microhardness on the location of the indent on the billet surface. The microhardness of the initial coarse grained alloy was close to that of the UFG samples measured on the plane normal to the extrusion axis. The tensile straining of samples in a wide temperature range of 4.2-295 K causes microhardness in the area of the neck to increase by more than 30%. The temperature dependence of microhardness in the interval of 77-295 K provides evidence for the thermally activated character of plastic deformation of alloy AZ31. The mechanism of deformation of the ECAP alloy is supposed to be the interaction of mobile dislocations with local obstacles, most probably associated with solutes.