Balance of mechanical properties of Mg-8Li-3Al-2Zn-0.5Y alloy by solution and low-temperature aging treatment

Abstract

In this work, solution and low-temperature (50–125 °C) aging treatment is utilized to develop a novel Mg-Li alloy with an excellent combination of strength and ductility. After optimizing the solution time, effects of aging treatment on microstructure and mechanical properties of the Mg-8Li-3Al-2Zn-0.5Y alloy were investigated. The highest strength is obtained after solution heat treatment at 350 °C for 4 h, accompanied with relatively low ductility. The following low-temperature aging treatment is used to balance the strength and ductility. With the increase of aging temperature, the ductility of the alloy was improved, accompanied by continued decrease in strength. The formation and aggregation of Al-Li phase during aging treatment is the major factor that influences the mechanical properties of the aged alloys. The reduced solid solution strengthening of Al and the aggregation of Al-Li phase are detrimental to strength. The evolution of Al-Li phase during aging treatment at different temperature is analyzed in detail. Through promoting the precipitation and preventing the aggregation of Al-Li phase by optimizing aging temperature, well-designed low-temperature aging treatment (75 °C × 4 h) results in favorable microstructural evolution and optimum combination of strength (yield strength = 216 MPa, ultimate tensile strength = 276 MPa) and ductility (elongation = 11.1%).