Influence mechanism of the keyhole behavior on penetration depth by in-situ monitoring in pulsed laser welding of aluminum alloy

The dynamic behavior of keyhole plays a critical role in determining the weld penetration and process stability during pulsed laser welding of thin-sheet aluminum alloy. This study aimed to explore the influence mechanism of the keyhole instability on the penetration depth under different pulsed laser parameters. To this end, we firstly applied a high-speed camera to directly observe the oscillation characteristic of inner keyhole through a transparent glass, and its fluctuation period was nearly coincided with one pulse duration. Based on maximum deviation ratio, the pulse frequency has a more obvious effect on the fluctuation in keyhole depth comparing with laser power and focus distance. Along with the increase of laser power and frequency, the incident laser intensity also increased, which leads to an increasing of keyhole depth and decreasing of inclination angle. The weld penetration depth is determined primarily by the variation of the keyhole depth and inclination angle. The findings of this paper will provide theoretical basis for achieving the desired weld penetration and improving weld quality regarding keyhole formation.