Structural homogeneity and low-temperature micromechanical properties of ultrafine-grained AZ31 magnesium alloy

The degree of microstructural homogeneity of ultrafine-grained (UFG) AZ31 magnesium alloy produced by a special thermomechanical process including four cycles of equal-channel angular pressing (ECAP, route B(c)) is studied by the microindentation method. The defect structure of the UFG alloy is quite homogeneous. Texture owing to ECAP showed up as a lower average microhardness measured in a plane perpendicular to the extrusion axis than that measured in a plane containing that axis, and in a slight dependence of the microhardness on the location of the indent on the billet surface. The microhardness of the initial coarse-grained alloy is close to that of the UFG samples measured in a plane perpendicular to the extrusion axis. Tensile deformation of the samples over a wide temperature range of 4.2-295 K increased the microhardness in the region of the neck by more than 30%. The temperature dependence of the microhardness over 77-295 K is indicative of thermally activated plastic deformation in AZ31 alloy. The mechanism for deformation of the alloy appears to be interactions between dislocations and local defects of impurity origin. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3624777]