AbstractLaser welds of electrical components made of highly conductive and light weight aluminum material are essential for the successful transformation of the energy and mobility sector towards renewable energy solutions. To generate a deeper understanding of this important laser welding process and to evaluate process dynamics, it is inevitable to use modern in situ analysis methods. In this work, in situ phase-contrast high-speed videography using synchrotron radiation is used for the first time to analyse the behaviour of different aspect ratios of the vapor capillary (capillary depth/focal diameter) on the stability and thus the porosity of laser welds. The phase contrast method reveals the phase boundaries between solid, liquid, and gaseous material phases and allows the quantitative analysis of the capillary depth and the porosity for different laser parameters and focal diameters. The study is based on the hypothesis that vapor capillaries with high aspect ratio are less influenced by the variation in the degree of energy coupling of the laser radiation, allowing a more stable process without the formation of pores. As result of the investigations, the welding processes with high aspect ratios show no formation of pores and thus higher capillary stability. A value for the aspect ratio of about 10 is identified as a geometric limit, above which pore formation in the processes no longer occurs. The findings are used to derive advice for a quality-specific process design in laser manufacturing processes of metallic materials.