Simulation and experimental studies of keyhole induced porosity in laser-MIG hybrid fillet welding of aluminum alloy in the horizontal position

•A unified model is developed for hybrid welding with horizontal fillet joint.•Formation process of bubble and porosity can be simulated directly.•Forward flow resulting from clockwise vortex is weakened in hybrid welding.•Keyhole collapses at its middle part easily, raising the possibility of generating large bubble.•The effect of welding current on keyhole behavior and weld porosity is discussed. The keyhole induced porosity in laser-MIG hybrid fillet welding of aluminum alloy in the horizontal position was investigated with simulation and experimental methods. A three dimensional model is developed, which takes into account geometric feature of horizontal filled joint and the coupling of keyhole, droplet and molten pool. Meanwhile, the major forces are also incorporated in the model. The inclination of heat source is dealt with through rotation of coordinate system. This model is able to calculate the keyhole dynamic behavior and the formation process of gas bubble as well as keyhole induced porosity directly. Also, it can describe the merging and disappearing of bubbles. The weld porosity was examined by the X-ray non-destructive testing. Large weld pool size provides more time for bubble to escape from the molten pool, which is the major factor responsible for the reduction in hybrid welding. Besides, the forward flow caused by the clockwise vortex is weakened, which also plays a positive role in improving the stability of back keyhole wall. The keyhole collapses at the middle part easily in horizontal fillet welding, raising the possibility of forming large pore. Bubble is easy to be captured by the upper weld pool boundary when floating up. With enhancing the welding current, the stability of keyhole is enhanced to some extent and the keyhole induced porosity is reduced.