Influence of low current auxiliary TIG arc on high speed TIG-MIG hybrid welding

Arc shape, droplet transfer, weld pool behavior and temperature fields were studied to investigate the influence of low current auxiliary TIG arc on weld formation and microstructure in TIG-MIG hybrid welding and compared with conventional MIG welding. Results indicated that the MIG arc is stabilized by a leading TIG arc while it is destabilized by a trailing TIG arc. Regardless of the TIG arc leading or trailing, it decentralized the MIG arc force and reduced the impingement of droplet. The backward fluid flow in the hybrid welding was decelerated relative to the conventional MIG welding. The slower backward fluid flow in hybrid welding impeded the accumulation of high temperature filler metal in the tail of weld pool and provided the molten metal more time to fill the weld toe which resulted in suppression of the undercut defect. The top surface temperature gradient at the middle and tail of the hybrid weld pool was lower than that in the MIG weld pool, albeit the welding heat input was increased. Microstructure analysis showed evidence of prominent dendrite formation at higher welding speeds with no obvious grain coarsening in the weld zone of TIG-MIG hybrid weld joint while its HAZ became narrower.