Microstructural evolution and mechanical properties of ZM6(Mg-Nd-Zr-Zn) alloy fabricated by wire arc additive manufacturing

Abstract

The wire arc additive manufacturing (WAAM) of Mg-Nd (rare-earth) alloys is of great significance for meeting the requirements of lightweight design and high manufacturing flexibility in large components. Thin walls of Mg-2.4Nd-0.3Zn-0.6Zr (ZM6, wt.%) alloy were prepared using the cold metal transfer (CMT)-WAAM process under three different parameters. The study focused on the forming quality, microstructure evolution and mechanical properties of the WAAM ZM6 alloy thin wall components. The results show that the thin-walled Mg alloy exhibits good formability with no obvious defects on the surface. Due to the influence of thermal cycling, the thin walls show a layered structure with alternating coarse and fine grains along the building direction. Furthermore, segregation of Mg₁₂Nd phase and Nd elements was observed along the α-Mg grain boundaries. The average grain sizes of fine and coarse equiaxed grains in the WAAM ZM6 alloy are 10.08 μm and 15.9 μm, respectively. From the bottom to the top, the hardness of ZM6 alloy thin-walled parts varies with the change of grain size, with an average hardness is 56.7 HV_0.2. The ultimate tensile strength in the traveling direction (TD) and building direction (BD) is 226 MPa and 214 MPa, indicating no significant anisotropy. Moreover, the elongation of the WAAM ZM6 Mg alloy reaches 15%, demonstrating good plasticity.