Influence of friction stir processing and aging treatment on microstructure and mechanical properties of wire arc additive manufactured Mg-Gd-Y-Zr alloy

This study systematically investigates the synergistic effects of wire arc additive manufacturing (WAAM), friction stir processing (FSP), and T5 aging on the microstructure and mechanical properties of Mg-9.54Gd-1.82Y-0.44Zr (GW92K) alloy. The as-deposited WAAM-GW92K alloy exhibits coarse equiaxed grains (∼16.4 μm) with brittle β-Mg₅(Gd,Y) eutectic networks and porosity (1.75 % volume fraction), resulting in limited strength (UTS=216 MPa) and ductility (EL=9.7 %). Multi-pass FSP (800 rpm, 50 % overlap) induces dynamic recrystallization (DRX), refining grains to 5.0 μm, reducing porosity by 89 %, and dissolving β phases into nano-β″/β′ precipitates (∼10 nm). Subsequent T5 aging (200°C/18 h) generates high-density prismatic β′ precipitates, achieving ultrahigh strength (UTS=336 MPa) but brittle fracture (EL=3.2 %) due to Orowan strengthening and dislocation blockage. The FSP-GW92K alloy demonstrates superior strength-ductility synergy (UTS=286 MPa, EL=13.1 %) through slip band coordination enabled by refined grains and coherent precipitates. Strengthening contributions are quantified via Hall-Petch (FSP grain refinement: 134.8 MPa) and Orowan mechanisms (β′ precipitates: 106.7 MPa) after T5 treatment. The FSP-induced dynamic dissolution-reprecipitation mechanism and Zr-assisted grain boundary pinning were identified as critical factors governing the transition from ductile dimple to brittle-ductile mixed fracture modes. These findings provide a novel pathway for fabricating high-performance Mg-RE components with tailorable strength-ductility trade-offs for aerospace applications.