Synchrotron X-ray imaging-based description of the effect of core-to-ring intensity distribution on the keyhole behavior in laser welding of die-cast aluminum

Laser deep penetration welding of die-cast aluminum presents challenges as the presence of retained gas under high pressure leads to a modified spatial and temporal keyhole behavior, which determines conditions for process pore formation. Currently different investigation with the goal manipulating the keyhole behavior focus on the use of adjustable core-to-ring intensity distributions. In wrought materials, a core-to-ring intensity distribution is referred to advantage a broader melt pool and enhance the keyhole width especially on the top, while only few investigations on welding of aluminum die-cast are reported. In this paper, investigation with in situ high-speed synchrotron X-ray imaging of a deep penetration laser welding process involving die-cast aluminum with different core-to-ring intensity distribution are presented. The results highlight a broadening of the keyhole width in the core-dominated process, while in the ring dominated process the keyhole width on the top is strongly reduced, leading to a pronounced bulging on the bottom of the keyhole. Further in the core-dominated process a second separated channel is formed beginning from the tip of the keyhole growing then in the rear part of it. This is then responsible for formation of a non-spherical cavity in the solidified pool. In the case of a ring-dominated regime bulging is occurring with mainly large bulging pores forming.