Enhancing forming quality, refining grains, and reducing anisotropy of mechanical properties of WAAM-processed AZ31 alloy by welding torch wobbling

The arc oscillation has a significant influence on the forming quality and mechanical properties of wire arc additive manufacturing (WAAM) process of magnesium alloy. In order to enhance the forming quality and mechanical properties of WAAM magnesium alloy components, arc oscillation was formed by wobbling welding torch during the process of WAAM with cold metal transfer method, and the impact of various wobble parameters on the formability, microstructure, and mechanical properties of WAAM-processed AZ31 magnesium alloy was studied. The results show that the WAAM-processed AZ31 alloy has a fully equiaxed crystal structure. Wobbling welding torch can increase the effective wall width and significantly improve the forming quality of WAAM. Arc oscillation induced by wobbling welding torch enhances the stirring effect and constitutional supercooling degree of melt pool and accelerates cooling rate of the WAAM-processed AZ31 alloy, therefore the grains in the deposition zone and the heat-affected zone can be refined. Simultaneously, wobbling welding torch significantly enhances the mechanical properties of the WAAM-processed AZ31 alloy. Compared no wobble with a wobble width of 10 mm and length of 4 mm, the grain sizes of the alloy in the deposition zone and heat-affected zone can be reduced by 12.3% and 14.9%, respectively, and the ultimate tensile strength and elongation in building direction increase from 225 MPa and 15% to 239 MPa and 25%, respectively. In addition, anisotropy of mechanical properties between the building direction and the traveling direction is significantly reduced. This study suggests that by adjusting welding torch wobble parameters during the WAAM of AZ31 alloy, it is possible to achieve a synergistic effect that simultaneously enhances the forming quality, reduces the anisotropy of mechanical properties, and improves the mechanical properties of the alloy.