High-strength Mg‐10Gd‐3Y‐1Zn‐0.5Zr alloy fabricated by wire-arc directed energy deposition: Phase transformation behavior and mechanical properties

Magnesium rare-earth (Mg-RE) alloys have great potential in lightweight applications because of the high specific strength. Wire-arc directed energy deposition (WA-DED) exhibits great prospects for the fabrication of large-scale monolithic structural components with high manufacturing flexibility. In this work, a single-pass multilayer Mg‐10Gd‐3Y‐1Zn‐0.5Zr (wt%, GWZ1031K) deposit was prepared via WA-DED. Electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are conducted to systematically explore the microstructural evolution during the WA-DED process and the subsequent heat treatment. The GWZ1031K alloy deposit fabricated by WA-DED exhibits uniform equiaxed grain structure whose average grain size is 22.3 ± 5.6 µm. The (Mg,Zn)3(Gd,Y) phase and RE segregation can be observed along the α-Mg grain boundaries (GBs). A number of needle-like γ ´ /γ ´ ´ phases embedded in the α-Mg grain interior (GI). In addition, there is a small number of fine RE-rich cubic phase and (Gd,Y)2O3 particles. The deposit shows significantly enhanced ductility and slightly improved strength after solution treated at 500 ℃ for 12 h. After the solution treatment, the intergranular (Mg,Zn)3(Gd,Y) eutectics dissolve into the matrix and long period stacking ordered (LPSO) phases precipitate from the GBs into the GI, contributing to the enhancement in ductility. Besides, the LPSO phase along with the existing RE-rich cubic phase, (Gd,Y)2O3 and Zr particles at GBs also play a role in hindering grain growth. The high-density nanoscale β ´ phases appear in the GI after aging treated at 200 ℃ for 24 h, resulting in the remarkable precipitation strengthening. In comparison with the solution-treated GWZ1031K deposit, the aging-treated exhibits a prominently improved ultimate tensile strength of 337 ± 7 MPa in the building direction (BD) and 331 ± 5 MPa in the travelling direction (TD). It is envisaged that the WA-DED manufacturing method will provide a simple and effective route to fabricate large-scale Mg-RE alloy components for various applications.