Effects of extrusion parameters on the microstructure and mechanical properties of Mg-Zn-(Mn)-Ce/Gd alloys

The effects of extrusion parameters on the microstructure and tensile properties of the Mg-2Zn-0.5Ce, Mg-1Zn-1Mn-0.5Ce, and Mg-2Zn-1.5Gd alloys were investigated by conducting indirect extrusion at different temperatures, ram speeds, and extrusion ratios. All of the extruded alloys exhibited a bimodal grain structure composed of equiaxed fine recrystallized (DRXed) grains and elongated coarse unDRXed grains, except for some alloys extruded at a high temperature and a fast speed. With an increase in the temperature, speed, and ratio of extrusion, the average size and area fraction of the DRXed grains increased as a result of the temperature rise at the deformation zone caused by deformation heating. The yield strength increased with a decrease in the size of the DRXed grains according to the Hall-Petch relation, while the elongation increased with an increase in the fraction of the DRXed grains due to the suppression of {10 - 11}-{10 - 12} double twinning, irrespective of alloy composition. Due to these relationships between the microstructural characteristics and tensile properties, the yield strength decreased but the elongation increased when the temperature, speed, and ratio were increased. (C) 2014 Elsevier B.V. All rights reserved.