Laser oscillation enables coordinated regulation of microstructure refinement and defect suppression in wire-feed laser directed energy deposited AZ91D magnesium alloy

Within the field of additive manufactured magnesium alloy, techniques such as laser powder bed fusion (LPBF), wire and arc additive manufacturing (WAAM) encounter difficulties in eliminate defects, including coarse columnar grains, porosity, and thermal cracks. To address these challenges, this study proposed an optimization framework for oscillation laser wire-feed directed energy deposited parameters tailored to AZ91D magnesium alloy. By employing a circular oscillation laser to introduce controllable molten pool agitation, the laser power was regulated to optimize the microstructure, mechanical properties, and corrosion resistance. The results showed that the porosity dropped from 1.85% to 0.12% as the laser power decreased from 1400 W to 1000 W. The grain size exhibited a tendency of initial increased followed by decreasing as the laser power ranged from 1000 W to 1400 W. Compared to the specimens at the laser power of 1000 W, grain size increased by 4.8% at 1200 W and decreased by 17.4% at 1400 W. Dispersed Al 8 Mn 5 and β-Mg 17 Al 12 phases are present in the deposited specimens. Simultaneously, high-density network of dislocations formed around the uniformly dispersed Al 8 Mn 5 phase. The corrosion rates at the laser power of 1200 W and 1400 W are 1.2 times and 3.2 times higher than that at 1000 W. The combined effects of grain refinement, dispersion strengthening by secondary phases and defect reduction enhanced the corrosion resistance in saline environments. Hence, an optimized balance of strength and ductility was achieved at a laser power of 1000 W, with an ultimate tensile strength of 303 ± 10 MPa, a yield strength of 160 ± 5 MPa and an elongation of 11 ± 0.4%. This study can offer actionable guidance for customizing the lightweight Mg alloy components with low porosity and desired microstructural features.