Dislocation structures in a near-isotropic Mg-Y extruded alloy

Deformation structures have been examined by transmission electron microscopy after 4% plastic deformation in tension and compression in a Mg-2.2 at%Y alloy extruded at 698 K to obtain a recrystallized grain size of about 20μm. The extruded alloy showed similar yield stresses of about 240 MPa in both tension and compression at room temperature. Dislocations formed by tensile stress showed a tendency of 〈a〉 type dislocations to cross slip to prismatic planes, resulting in long continuous dislocation loops. Dislocation loops with 〈c〉components were also observed. Occasionally, {101¯2} type twinning was also observed in grains with large orientation away from basal texture. These grains contained predominantly basal slip. Compression deformed samples showed a limited number of {101¯2} type twins. The matrix contained loops of non-basal 〈a〉 type dislocations, together with basal dislocations with 〈c〉 component. Inside the twins occurred stacking faults and loops of 〈c〉 type dislocations with segments perpendicular to the basal plane. Activation of several deformation modes and complex dislocation structures explains the strain hardening behavior and low anisotropy of the alloy.