Effect of Mn content on microstructure, texture and room temperature mechanical properties of hot-extruded Mg-2Nd-1Gd alloy

The effect of the Mn content on microstructure, texture and room temperature mechanical properties of hot-extruded Mg-2Nd-1Gd alloy was investigated. It was found that the microstructure of hot-extruded Mg-2Nd-1Gd-xMn (x=0, 0.25 and 0.5, wt%) alloys was primarily composed of fine-grained α-Mg matrix phase and point-like streamline-distributed Mg₄₁(Nd, Gd)₅ phase along the extrusion direction. Mn element in the extruded Mg-2Nd-1Gd-0.25Mn and Mg-2Nd-1Gd-0.5Mn alloys was mainly distributed as solid-solution Mn atoms and α-Mn particles, respectively. With increasing Mn content, the recrystallization fraction of Mg-2Nd-1Gd-xMn alloys increased from 79% to 94.3% and then decreased to 77.8%. Meanwhile, the average grain size first increased from 7.9 μm to 11.9 μm, and then decreased to 7.5 μm. Microstructure characterization revealed that solid-solution Mn atoms in extruded Mg-2Nd-1Gd-0.25Mn alloy reduced the segregation of Nd and Gd, consequently weakening the solute drag effect. In contrast, α-Mn particles pinned grain boundary and then delayed recrystallization process in extruded Mg-2Nd-1Gd-0.5Mn alloy. The extruded Mg-2Nd-1Gd and Mg-2Nd-1Gd-0.25Mn alloy exhibited a typical rare-earth texture, while the extruded Mg-2Nd-1Gd-0.5Mn alloy exhibited a basal texture along with a rare-earth texture due to the presence of deformed grains. Among extruded Mg-2Nd-1Gd-xMn alloys, the extruded Mg-2Nd-1Gd-0.5Mn alloy exhibited excellent room temperature mechanical properties, with the yield strength of 138.0 MPa, ultimate tensile strength of 231.1 MPa, and elongation of 38.8%. Further quantitative analysis revealed that the grain boundary and dislocation strengthening were the main factors affecting the yield strength of extruded Mg-2Nd-1Gd-0.5Mn alloy, accounting for 44% and 24.1%, respectively.