Additive manufacturing high-strength and ultra-high-rare-earth magnesium alloys: Excellent long-time aging hardening and strengthening behavior
Zhe Xu, Zhuo Li, Chunjie Shen, Dongdong Zheng, Yuxuan Tu
Abstract
Gadolinium (Gd) is one of the most effective strengthening elements for magnesium alloys. The development of commercially available Mg-Gd alloys with high Gd content and the optimization of their preparation processes have been a major focus in magnesium alloy research. In this study, a Mg-23Gd-2Zn-0.4Zr alloy with ultra-high Gd content is designed, and high-quality fabrication is achieved using laser-directed energy deposition (LDED) technology. Through heat treatment and microstructure control, a balance between tensile strength (425 MPa) and elongation (3.4 %) is achieved. The ultra-high strength of the LDED-T6 VZ232K alloy is primarily attributed to precipitation strengthening caused by the ultra-high density (2.4 × 10 4 µm -2 ) of β′ phase. The high ductility is mainly due to the modification of the fracture mode, facilitated by the introduction of a substantial number of stacking fault structures during solution heat treatment. The extended hardness plateau (exceeding 138 Hv) and high yield strength (exceeding 300 MPa) are associated with the three-directional cross-interlocked structure of the β′ phase in the over-aged state at 220 °C and 250 °C. The analysis of the LDED-VZ232K alloy indicates that reduced heat input during the additive manufacturing (AM) process is critical for the defect-free fabrication of alloys with ultra-high Gd content.