Influence of deposition strategy-regulated thermal field distribution on the microstructure and mechanical properties of thick-walled AZ31 magnesium alloy parts fabricated by WA-DED

Driven by the global demand for lightweighting, magnesium alloys have great appeal in the manufacturing of large components. Although wire arc directed energy deposition (WA-DED) enables rapid fabrication of components, the severe mechanical anisotropy caused by the steep heat gradient remains a core bottleneck for engineering applications. Therefore, this study systematically investigated the influence mechanisms of alternate (A-DS), orthogonal (O-DS), serpentine (S-DS) and zigzag (Z-DS) deposition strategies on the microstructure evolution and mechanical properties of thick-walled block AZ31 magnesium alloy parts fabricated via cold metal transfer (CMT). Combined with finite element thermal field simulations, the regulatory effects of deposition strategies on the spatial distribution of heat input and cooling conditions were systematically analyzed. The results reveal that deposition strategies exert a remarkable effect on grain size and basal texture intensity. Among them, A-DS effectively dispersed the heat input, resulting in the smallest average grain size and the weakest basal plane texture; while the Z-DS with directional distribution of heat flow led to the strongest preferred orientation. The results of the tensile test further reveal that the anisotropy of the parts is highly dependent on the deposition strategy. The O-DS sample exhibited the highest ultimate tensile strength in the middle of the travel direction, at 265 ± 5.2 MPa; however, its mechanical properties in the build direction were the poorest. On the contrary, the A-DS sample promoted repeated fragmentation of large particles through a 180° alternating scanning strategy and mitigated interlayer tensile stress, resulting in the highest mechanical performance along the build direction, with an ultimate tensile strength of 254 ± 3.9 MPa and an elongation of 21.5 ± 0.4%. The Z-DS sample exhibited better elongation rates in different height directions. This study indicates that by optimizing the deposition strategy to precisely control the thermal field distribution, it is a key approach to improving the microstructure of WA-DED magnesium alloys and effectively alleviating the mechanical anisotropy.