Cooperative achievement in grain refinement and texture weakening of Mg-Gd-Y-Sm-Zr alloy fabricated by asymmetric extrusion-shear process

Mg-Gd-Y-Sm-Zr alloy with fine grains and weak texture was fabricated by extrusion -shear (ES) process. The microstructure evolution mechanism of the alloy during asymmetric plastic deformation process was analyzed. At the forward extrusion stage, the initial coarse grains are refined significantly under the synergistic action of discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX), and deformation bands (DBs) induced dynamic recrystallization (DRX). The shear deformation during equal channel angular pressing (ECAP) can further refine the residual coarse grains after the previous extrusion, as well as weaken the basal texture of the alloy. The effect of extrusion ratio (lambda = 9, 16, 25, 36) on the alloy after ES forming was studied. When lambda is 25, the component has superior mechanical properties with yield tensile strength (YTS) of 216 MPa, ultimate tensile strength (UTS) of 303 MPa and elongation of 25.47%. The improvement of YTS after ES forming is mainly attributed to the grain boundary strengthening, while the excellent elongation is benefited from the weak bimodal texture. Abnormal grain growth will occur when lambda is 36, leading to a decrease in the strength and plasticity of the alloy.