Microstructure and mechanical properties of ultra-light Mg–8Li–3Al–2Zn–0.5Y alloy manufactured by directed energy deposition-Arc

The ultra-light Mg–8Li–3Al–2Zn–0.5Y (LAZ832–0.5Y) thin wall parts with excellent performances were successfully fabricated by Gas Tungsten Arc Welding (GTAW) in this study. The microstructure of the top, middle and bottom regions of the thin wall fabricated under various conditions was examined and the mechanical properties of these thin walls were tested. The results showed that much finer microstructure was obtained by GTAW than that made by conventional casting method. In the as-deposited samples, the needle-like shaped α-Mg phase emerged at the top of the thin wall whereas the bar-shaped α-Mg phase showed up in the middle and bottom regions of the thin wall due to the complex thermal history. The Al₂Y phase was dispersed throughout both α-Mg and β-Li while the AlLi phase was mainly located in the β-Li. The best combination of ultimate tensile strength (UTS), yield strength (YS) and elongation to fracture of the as-deposited thin wall were 218.9 MPa, 171.4 MPa and 20.9%, respectively, which was manufactured under the optimal condition of 120 A 1800 mm/min 220 mm/min. After solid solution treatment at 350 °C for 4 h, the UTS increased slightly by 13% but the YS increased significantly by 65% compared with the samples before solid solution. The solution of the AlLi phase was believed to be the main strengthening mechanism. It is interesting to note that the UTS and YS of the as-deposited sample was better than those of the as-cast sample while the opposite situation took place after solid solution treatment.