Mg–Gd–Y–Zn–Zr Alloys Fabricated by CMT Arc Additive Manufacturing: Processing, Microstructure Refinement and Property Analysis

This study investigated the relationships among pore evolution, microstructural refinement, and mechanical performance in Mg–Gd–Y–Zn–Zr alloys fabricated by cold metal transfer arc additive manufacturing. Droplet-transfer simulations suggest that pores formed during deposition may migrate within the molten pool and escape under intensified melt convection conditions. This behavior is likely associated with enhanced molten-pool convection, prolonged liquid-phase residence time, and a reduced bubble escape distance, which collectively facilitate pore removal. Microstructural characterization indicates a moderate grain refinement effect under the high-heat-input condition, with the average grain size decreasing to approximately 6.32 μm. The observed refinement behavior appears to be related to the fragmentation and redistribution of Zr-rich clusters originating from the filler wire. The dispersed Zr particles promote the formation of fine (Gd,Y)H2 phases and act as effective heterogeneous nucleation sites, thereby markedly increasing the nucleation density during solidification. In-situ tensile EBSD analysis indicates that the reduction of continuous networked grain-boundary secondary phases weakens the constraint of the brittle boundary skeleton, allowing tensile stress to be more effectively transferred into the α-Mg matrix and promoting intragranular lattice rotation, basal slip activation, and \10\bar12\ tensile twinning. The strength–ductility synergy originates from the combined effects of pore elimination, grain refinement, optimized grain-boundary secondary-phase distribution, dislocation pinning by intragranularly dispersed (Gd,Y)H2 particles, and sustained basal slip activation assisted by tensile twinning. Consequently, the alloy achieves an ultimate tensile strength of 328±4 MPa and an elongation of 7.27±0.4%.