Strength improvement achieved by microstructure regulation for wire-arc directed energy deposited Mg-Li alloy

Abstract

Here we fabricate LA103Z Mg-Li alloy via wire-arc directed energy deposition (WA-DED), and subsequent aging treatment is employed to improve its mechanical property. Results show that a typical dual-phase microstructure is formed upon WA-DED, consisting of α-Mg, β-Li, AlLi and Li₂MgAl, with negligible porosity, and the core-shell Li₂MgAl/AlLi composite particles are also generated. After aging treatment, the microstructure is slightly coarsened, together with the precipitation of nano-sized D0₃−Mg₃Al particles, as well as the dissolution and the mergence of α-Mg phases. Negligible strength and ductility anisotropies are found for the as-deposited alloy. Significant strength increment is achieved via aging treatment, and the ultimate strength increases by ∼20% (∼34 MPa), reaching 200±1 MPa. Both as-deposited and aged alloys show acceptable uniform elongation, with a transgranular fracture mode. Precipitation strengthening enabled by nano-sized D0₃−Mg₃Al precipitates is primarily responsible for the strength increment mediated by aging treatment. Grain refinement strengthening and solid solution strengthening provide additional contributions to the improved strength. Our work thus offers an applicable additive manufacturing pathway for the efficient and safety-guaranteed fabrication of Mg-Li alloy components with decent mechanical property.