High Strength and Low Yield Anisotropy of Hot-Extruded Mg-2.35Nd-1.32Gd-0.18Zn-0.32Zr Alloy Sheet via Cold Rolling and Subsequent Aging Heat Treatment

Abstract

In the article, microstructure, texture, and room-temperature mechanical properties of the hot-extruded Mg-2.35Nd-1.32Gd-0.18Zn-0.32Zr alloy sheet subjected to cold rolling and subsequent aging heat treatment are investigated. It is found that the extruded experimental alloy sheet exhibits homogeneous microstructure and extrusion direction-split texture, and approaching room-temperature mechanical properties along extrusion and transverse directions. The rare-earth texture component deflects toward the basal texture component, resulting in a relative mitigation of texture differences between extrusion and transverse directions after cold rolling. Subsequent aging heat treatment significantly alleviates severe stress concentration near the grain boundaries, and precipitates many fine β₁ phase within grains. The yield strength and ultimate tensile strength in the extrusion direction of extruded experimental alloy sheet significantly increase from 150 and 230 MPa to 312 and 347 MPa after cold rolling and subsequent aging heat treatment, respectively. Meanwhile, the yield strength ratio between extrusion and transverse directions improve from 0.92 to 1.03, which is mainly attributed to the texture evolution and the different strengthening effects of the β₁ precipitates on basal <a> and prismatic <a> dislocations. Grain boundary and precipitation strengthening are inferred as the dominant strengthening mechanisms, accounting for about 75% to the yield strength.