Effects of heat source arrangements on Laser-MAG hybrid welding characteristics and defect formation mechanism of 10CrNi3MoV steel

Laser-MAG hybrid welding 10CrNi3MoV steel was fabricated with different arrangements (the leading mode, and distance between laser beam and electrode tip (D-LA)). Welding characteristics and defect formation mechanisms were investigated by high-speed images (HSI) and real-time electric signals. Arc behaviors, droplet transfers and defects (pores, undercut and spatters) were observed with the increased D-LA in arc leading mode and laser leading mode. electric signals and HSI observations revealed that the leading mode and D-LA significantly affected the welding characteristics (Weld morphologies, process stability and droplet transfer) and defect formation. For two leading modes, stable welding process and sound welded formation was achieved by adjusting D-LA = 2-4 mm. Synergistic effect of laser and arc made the arc stabilize and droplets transfer smoothly and steadily in projected transfer mode. And the final weld morphology for arc leading mode was superior to one for laser leading mode. As D-LA increased, defects began to form. Arc leading mode was susceptible of pore and undercut formation. Because the increased D-LA provoked the irregular molten metal movement, leading to keyhole collapse, and caused the previous solidified layer rim hinder the center molten metal to fill the weld toe. While Laser leading mode was susceptible of spatter formation since the increased D-LA caused the swelling formation by the arc forces and droplets impact on the back wall of the keyhole, and the swelling was collided by laser evaporation reaction and formed liquid column, final disintegrating into spatters.