Stability enhancement of molten pool and keyhole for 2195 Al Li alloy using fiber-diode laser hybrid welding

Molten pool and keyhole stability are vital concerns in laser welding of 2195 AlLi alloy, potentially affecting the weld quality and porosity defect. Fiber-diode laser hybrid welding, which coaxially superimposes dual laser beams with different wavelengths and spot diameters, is superior in improving welding stability and quality. In this paper, the molten pool dynamic characteristics associated with the keyhole during fiber-diode laser hybrid welding were innovatively investigated to explore the impact of different laser energy on welding stability. The inner keyhole was observed by utilizing the "sandwich" structure with 2195 AlLi alloy and refractory glass. The experimental results indicate that during fiber-diode laser hybrid welding, a larger molten pool and plasma plume, deeper keyhole depth, and smoother keyhole rear wall are generated compared to single fiber laser welding. It is shown that the closing of the keyhole entrance and the swelling of the molten pool are effectively inhibited due to the superposition of the diode laser. The average keyhole depth during fiber-diode laser hybrid welding at the PD of 2500 W is substantially increased compared to that during single fiber laser welding. Based on the keyhole and molten pool characteristics, the mechanism of stability enhancement with the assistance of a diode laser is understood. In addition, the fiber-diode hybrid welding method can achieve a weld seam (WS) with high-quality surface morphology and a low porosity ratio of 0.7 %. This work provides the necessary theoretical basis and technical guidance for the fiber-diode laser hybrid welding technology of aluminum alloy.