Characteristic of keyhole, molten pool and microstructure of oscillating laser TIG hybrid welding

In this research, the dynamic change of laser keyhole of vertical oscillating laser keyhole was studied, and it was found that the laser keyhole depth was periodic. The keyhole depth decreased with the increase of oscillation amplitude and frequency, but the stability of the keyhole increased. This was closely related to the energy distribution of oscillating laser. The special energy distribution made the “two molten pools“ phenomenon appear in oscillating laser tungsten inert gas (TIG) hybrid welding, and the grains in the keyhole molten pool were smaller than those in the conduction molten pool. The narrow gap (NG) oscillating laser TIG hybrid welding (OL-T) was carried out, and the microstructure and mechanical properties of OL-T welding were compared with that of TIG welding and general laser TIG hybrid welding (L-T). The grain of the OL-T welding seam was refined because the OL-T welding had a lower line energy, which changed the crystalline morphology of the welding seam. The tensile strength of the weld joint was almost equivalent to that of TIG welding and base metal, reaching 559 MPa. It was observed that there was no lack of sidewall fusion in the welding seam of the NG OL-T welding, and the weld efficiency was much higher than that of TIG welding. The morphology of the molten pool in oscillating laser-TIG hybrid welding and the arc shape in the groove were collected using high-speed cameras. It was observed that the elimination of lack of sidewall fusion in NG welding mainly depended on the direct heating on the sidewall and stirring molten pool by oscillation laser.