Wire arc additive manufacturing of a Zn-containing magnesium rare-earth alloy: Heat treatment process, mechanical properties and phase transformation behavior

This study investigates the wire arc additive manufacturing (WAAM) of a Zn-containing rare-earth magnesium alloy (Mg-7Gd-3Y-1Zn-0.5Zr, designated GWZ731K), focusing on its heat treatment processes, mechanical properties, and phase transformation behavior. WAAM, known for its safety and efficiency in fabricating GWZ731K alloy parts, was employed along with a customized ultrasonic frequency pulsed arc for depositing alloy in this research. A thermodynamically guided short-time solution treatment process (STSP) was developed and compared with a conventional long-time solution process (LTSP), both followed by aging. Mechanical testing revealed that both STSP + aging and LTSP + aging treatments enhanced tensile strength (∼320–330 MPa), while STSP-treated alloys exhibited significantly improved ductility (∼6–7 %) compared to LTSP-treated alloys (∼3–4 %), achieving a superior strength-ductility synergy. The as-deposited alloy exhibited homogeneous fine equiaxed α-Mg grains with weak basal texture, along with eutectic structures and long-period stacking ordered (LPSO) phases. The optimized heat treatment regime can successfully prevent grain coarsening while achieving effective dissolution of RE-rich eutectics. Microstructural analyses using SEM, EBSD, and TEM confirmed that heat treatment dissolved eutectics and promoted the formation of fine β′ precipitates and thermally stable 14H-LPSO phase. A high density of stacking faults served as nucleation sites for LPSO phases, with evidence of 18R-to14H-LPSO phases transformation during heat treatment. Quantitative analysis of strengthening mechanisms indicated that grain refinement, solid solution, and precipitation collectively contributed to the alloy's mechanical performance. This research demonstrated that a thermodynamically optimized STSP + aging regime effectively enhances performance of WAAM-prepared Mg-RE alloys while aligning with rapid manufacturing principles. This work offers critical insights for advancing WAAM technologies and broadening the application of Mg-RE alloys in lightweight structural components.