Correlative high-speed synchrotron X-ray and inline coherent imaging of high-power laser welding

Abstract High-power laser welding is central to electric vehicle (EV) manufacturing, yet keyhole instability and associated defects remain difficult to control due to highly transient process dynamics. Here, we combine inline coherent imaging (ICI) and high-speed synchrotron X-ray radiography (up to 1 MHz) to resolve process dynamics under EV-relevant welding conditions. Single-mode (SM) beams produce deep, narrow keyholes (depth-to-width ratio of ~15:1) and enable greater penetration than multi-mode (MM) beams. When penetration depth is matched, the narrow keyhole geometry suppresses large collapse cavities and promotes rapid re-opening of transient liquid bridges under single-mode conditions, resulting in lower porosity than multi-mode welding. Adding a ring-mode beam improves surface finish and keyhole stability by suppressing rear-wall bulging, resulting in lower porosity. ICI measurements show excellent agreement with X-ray-derived keyhole depths under SM and MM welding, validating ICI for in situ depth measurements. Our work provides quantitative guidance for beam-profile-dependent depth monitoring and defect mitigation under EV-relevant laser-welding conditions.