Mechanism analysis on suppressing porosity in laser-MIG hybrid welding of aluminum alloy via external magnetic field

An external magnetic field with a high magnetic flux density (≥300 mT) has been proven to reduce the porosity of aluminum alloy single laser welded joints. However, the additional welding current exists in laser-arc hybrid welding (LAHW) and its physical mechanism of interaction between the external magnetic field and the molten pool is different from magnetic-assisted laser welding. It was explored whether the porosity suppression of the external magnetic field works in LAHW using experimental observation and numerical simulation. The results suggested that the presence of an arc would induce the interaction between the magnetic field with a lower magnetic flux density and welding current, giving rise to a strong backward Lorentz force up to 1.44 × 105 N/m3, which differed from that in the magnetic-field-assisted laser welding. Although the presence of an arc heat source extended the solidification time of the rear weld pool. The impact of the droplet on the rear keyhole wall deteriorated the keyhole stability and caused severe keyhole collapse. Additionally, some vortices also deformed the keyhole rear wall and prevented the escape of bubbles in LAHW, leading to a greater porosity rate of 13.7 %. However, the impact of the droplet was weakened and vortices were reduced when an external magnetic field of 24 mT was used, which significantly decreased the porosity rate of LAHW to 2.0 %. This study will provide a more underlying understanding of magnetic-field-assisted welding and widen the industrial application of LAHW.