Arc mode governed droplet transfer in wire-arc directed energy deposited GW102K alloys: A pathway to manipulating microstructure and mechanical response

Wire-arc directed energy deposition (WA-DED) holds promise for fabricating large-sized magnesium alloy components. However, its widespread adoption is limited by the formation of coarse columnar grains and associated defects, which impair mechanical performance and introduce anisotropy. As a critical process parameter governing droplet transfer behavior, the arc mode offers a viable approach to manipulating microstructure and mechanical response. Herein, the results demonstrate the fabrication of components with a porosity below 0.1‰, fully equiaxed grains, and isotropic properties in the WA-DED GW102K magnesium alloy, which underscores the superiority of the cold metal transfer (CMT)-based arc modes for fabricating high-performance magnesium alloys. Critically, the arc mode serves as a decisive factor in controlling solidification and microstructure through its unique thermal and droplet transfer dynamics. The resulting microstructural characteristics, including grain size, precipitates, and dislocation networks, directly account for the differences in mechanical performance. The samples fabricated with the pulsed CMT (CMT-P) mode exhibited the highest strength yet the lowest ductility, which is attributable to an elevated residual dislocation density coupled with the large and irregular defects. In contrast, those deposited by the CMT mode achieved an optimal balance between strength and ductility, demonstrating a high ultimate tensile strength of 244 MPa and an elongation of 7.5%. The strength is governed by a combination of contributions from the grain boundaries, eutectic phases, solid solutions, dislocations, and nanoprecipitates. Theoretical calculations reveal that grain boundary strengthening provides the dominant contribution. This work thus establishes a novel pathway for fabricating isotropic magnesium alloys with good properties, by manipulating the arc mode to tailor both microstructure and mechanical performance.