Effect of laser power on stability of pulsed laser-arc hybrid welding process for 6082-T6 aluminum alloy

In this study, the effect of laser power on the stability of pulsed laser-MIG hybrid welding (PLMHW) process for 6082-T6 aluminum alloy was studied. The porosity of weld metal (WM) was significantly reduced by 2.35 % at the laser power of 5.4 kW (P_5.4); and the welded joints were more well formation and no obvious defects. The formation of pores in the welding process was related to the arc electrical signal, which affects the droplets transfer. The results showed that the electrical signals of laser power 5.0 kW (P_5.0) and laser power 5.8 kW (P_5.8) fluctuate greatly, while P_5.4 was more stable. The droplets transfer modes of P_5.0 and P_5.8 were “one pulses-two droplets” and “two pulses-one droplet”, respectively, which affected the keyhole stability. At P_5.4, the droplets size was moderate, the heat input was reasonable, and the transition frequency was stable, showed “one droplet-one pulse”, which helped to reduce keyhole fluctuations, promote gas escape, and reduced porosity. The results of microhardness showed that the hardness of WM, heat affected zone (HAZ) and base metal (BM) was about 77 Hv, 85 Hv and 95 Hv respectively. The hardness increased from WM to BM, and the hardness of weld center was the lowest due to coarse dendrite. The tensile strength of P_5.4 welded joint at room temperature was 235.62 MPa, the yield strength was 159.57 MPa, and the elongation was 14.29 %. Scanning electron microscopy (SEM) showed that the tensile fracture of P_5.0 and P_5.8 had less dimples, cleavage planes and tearing edges, and the joint performance was poor. PLMHW was applied to 6082-T6 aluminum alloy to investigate the influence of laser power variations on welding process stability. This study provided additional guidance for optimizing processing parameters in PLMHW and established correlations between droplet transfer modes and welded joint performance.