Vacuum laser beam welding characteristics for aluminum alloys and its effects on plasma plume generation and laser weldability

The laser weldability of aluminum alloy is unstable due to low laser beam absorption rate, low viscosity, and high thermal diffusivity. As a result, defects such as porosity and sagging are easily formed in the fusion zone. Vacuum laser beam welding (VLBW) has been introduced to ensure better weldability by using a relatively low ambient pressure. This allows for deep penetration depth and stable keyhole behavior compared to welding under atmospheric conditions. To evaluate the effects of ambient pressure on laser welding characteristics, VLBW was performed with similar and dissimilar aluminum alloys. Varying the pressure inside the vacuum chamber affected the welding characteristics. It is inferred that variation in ambient pressure changes the interactions between the laser source and substrate, such as the laser energy transfer, plasma plume generation, and the behavior of keyhole and molten pool. The penetration depth increased with decreasing ambient pressure for the same heat input conditions. Also, decreasing the ambient pressure reduced the formation of defects such as sagging, underfill, and porosity. Plasma plume generation was also varied depending on the ambient pressure, and plasma plume height and intensity were compared using a CCD camera. In this experiment, an ambient pressure of 10 mbar was sufficient to ensure good welding properties and stability. Below 10 mbar, the VLBW system is considered an effective alternative to processes that require high vacuum environments.