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

Abstract

The effect of Mn content on the microstructure, texture, and room-temperature mechanical properties of hot-extruded Mg–2Nd–1Gd alloy was investigated. The microstructure of hot-extruded Mg–2Nd–1Gd–xMn (x = 0, 0.25wt%, and 0.5wt%) alloys consisted primarily of a fine-grained α-Mg matrix phase and point-like, streamline-distributed Mg₄₁(Nd,Gd)₅ phase along the extrusion direction. In the extruded Mg–2Nd–1Gd–0.25Mn and Mg–2Nd–1Gd–0.5Mn alloys, Mn was mainly present as solid–solution Mn atoms and α-Mn particles, respectively. With increasing Mn content, the recrystallization fraction of the 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 to 11.9 µm and then decreased to 7.5 µm. Microstructural characterization revealed that the solid–solution Mn atoms in the extruded Mg–2Nd–1Gd–0.25Mn alloy reduced the segregation of Nd and Gd, thereby weakening the solute drag effect. In contrast, α-Mn particles pinned the grain boundaries and delayed the recrystallization process in the extruded Mg–2Nd–1Gd–0.5Mn alloy. The extruded Mg–2Nd–1Gd and Mg–2Nd–1Gd–0.25Mn alloys exhibited a typical rare-earth texture, whereas the extruded Mg–2Nd–1Gd–0.5Mn alloy displayed a basal texture combined with a rare-earth texture due to the presence of deformed grains. Among the extruded Mg–2Nd–1Gd–xMn alloys, the Mg–2Nd–1Gd–0.5Mn variant exhibited the best room-temperature mechanical properties, with a yield strength of 138.0 MPa, an ultimate tensile strength of 231.1 MPa, and an elongation of 38.8%. Quantitative analysis indicated that grain boundary and dislocation strengthening were the main contributors to the yield strength of the extruded Mg–2Nd–1Gd–0.5Mn alloy, accounting for 44% and 24.1%, respectively.

Keywords

hot-extruded Mg alloy / Mn addition / microstructure / texture / strengthening mechanisms / mechanical properties

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