Dependence of the mechanical properties and microstructure of ultralight magnesium-lithium-aluminum alloy on heat treatment conditions

Magnesium-lithium-based alloys demonstrate lower densities and superior workability than conventional magnesium alloys. Their mechanical properties are required to be improved. In this study, the effect of heat treatment conditions on the mechanical properties and microstructure of magnesium-lithium-aluminum alloys were investigated. Material used in this study is LA143 (Mg-14.4%Li-2.8%Al). Specimens are machined from alloy sheet, and heat-treated at 523K and 573K for 1 or 100h in argon atmosphere. Tensile tests showed that the yield stress, ultimate tensile strength, and total elongation significantly depend on the heat treatment. Figure. 1 shows yield strength and Vickers hardness as a function of d^-1/2 (d : grain size). The relationship between the yield stress and grain size was not governed by traditional Hall-Petch relationship. The activation volume of various heat-treated samples estimated from the strain rate jump test was smaller for higher yield stress. Wide-angle X-ray scattering indicated that the second phase with a Bragg spacing of 1.7nm was generated after heat treatment. This second phase periodic structure affects the mechanical properties of the magnesium-lithium-aluminum alloy. We believe the results contribute to further improvements in the mechanical properties of Mg-Li-based alloys.