Molten pool dynamic behavior simulation in vertical ultrasonic vibration laser welding of 7075 aluminum alloy

Ultrasonic vibration laser welding is an emerging welding technology that can effectively suppress the formation of weld porosity in aluminum alloys. However, the effect of ultrasonic vibration on the dynamic behavior of the molten pool is unclear. In this study, the molten pool dynamic behavior during vertical ultrasonic vibration laser beam welding of 7075 aluminum alloy was simulated. The results show that in non-vibration welding, positive pressure appears in the front of keyhole, which makes the keyhole form a wasp-waist-like structure and easily break into small parts. In vibration welding, positive pressure appears at the bottom of keyhole, and the average value of positive pressure decreases and then increases when the vibration frequency of the laser beam focus increases from 20 to 50 kHz. This pressure distribution makes the keyhole more stable and inhibits the formation of pores. However, too high vibration frequency of the laser beam focus may have a negative effect on the keyhole formation. The results of the study help to understand the mechanism of the formation of porosity during the ultrasonic vibration laser beam welding process.