Designing high modulus Mg-Li alloy by forming heterostructures resistant to age softening due to Ag diffusion drags

Mg alloy accounts for the second largest production of non-ferrous alloys after Al alloys in the world. However, the intrinsic low strength and elastic modulus limits its further applications in critical structural components. In this study, Ag has been found to promote the formation of heterostructures of BCC β-Li layers. It contributes to grain boundary strengthening as well as precipitation strengthening. In addition, it activates more slip systems than the HCP α-Mg during plastic deformation. CPFEM simulations and TEM experiments have identified its deformation mechanism. First-principles calculations and nanoindentation experiments demonstrate that Ag doping improves the stability, bulk modulus, and shear modulus of the β-Li phase and the MgLi₂Zn precipitates. The high modulus Al₂RE and β-Li phases increase the elastic modulus of the alloy. Consequently, the strength, stiffness, and ductility of the alloy are improved by the heterostructure of β-Li and hard precipitates.