Enhanced high-temperature mechanical properties of wire-arc directed energy deposition Mg-6Gd-3Y-0.4Zr alloy via aging treatment: Microstructural evolution and strengthening mechanisms

This study systematically explored the microstructure evolution and mechanical properties of Mg-6Gd-3Y-0.4Zr (VW63K) alloy fabricated by wire-arc directed energy deposition (WA-DED). In the as-deposited condition, the alloy exhibited refined equiaxed grains with a mean grain size of approximately 21.9 μm and relatively weak crystallographic texture. Aging treatment promoted significant precipitation of Mg₃Gd phases, effectively enhancing the ultimate tensile strength (from 241 to 300 MPa), but reducing ductility (elongation, from 16.8% to 4.0%) at room temperature. Subsequent tensile testing at 200°C after aging treatment resulted in further grain growth (27.7 μm) accompanied by twin formation, and dislocation rearrangement, thereby leading to a synergistic improvement in strength (ultimate tensile and yield strengths of 312 and 195 MPa, respectively) and ductility (elongation of 8.7%). Fracture morphology transitioned from ductile-dominated to mixed ductile-brittle mode upon aging, and returned to predominantly ductile model under high-temperature condition. These findings elucidated the critical roles of precipitation as well as twinning-induced strengthening in enhancing high-temperature properties of WA-DED VW63K alloys.