Penetration, porosity prevention mechanism and welding phenomena in laser-arc hybrid welding

Summary form only given. Hybrid welding of stainless steels and aluminum alloys was performed with the heat sources of YAG laser and TIG, and YAG laser and MIG respectively. The effects of welding conditions and melt flows on penetration depth, weld bead geometry and porosity formation tendency were investigated with high-speed video observation and X-ray transmission real-time observation methods. The penetration depth was affected not by the arc current but by the laser power in TIG-YAG hybrid welding of stainless steel. On the other hand, the penetration was affected by the arc current in MIG-YAG hybrid welding of aluminum alloys. In both hybrid-welding processes, the beneficial conditions for the production of the deepest penetration were established. Moreover, the target distances between the laser beam and the electrode or wire exerted a great effect on the penetration and its geometry. The great effect of downward melt flows induced by recoil pressure against the keyhole wall and by surface tension and electromagnetic force due to the arc constriction in the molten pool on the penetration depth and geometry were consequently confirmed. Concerning porosity suppression, in YAG-TIG hybrid welding of stainless steel, no porosity formation was attributed to the generation of no bubbles from the tip of a keyhole produced with a laser beam. On the other hand, at high currents in MIG-YAG hybrid welding of aluminum alloys, disappearance of bubbles from the concave molten pool surface played an important role of reduced porosity