The video shows a synchrotron x-ray video of full-penetration laser welding of the aluminum alloy AA1050A (Al99.5). At the beginning of the video the transition from partial penetration welding with a keyhole which is closed at its bottom to full-penetration welding with a keyhole which is opened at its bottom can be observed. The images show that the fluctuations of the capillary’s geometry during the beginning of the process result in an excessive formation of pores. During the further progress of the process a reliable full-penetration process is achieved with an increased stability of the geometry of the keyhole. A detailed analysis of this transition and its implications on the absorptance are presented in the related publication.

The presented investigations were carried out in cooperation with DESY in Hamburg and with RWTH Aachen University within the framework of the Collaborative Research Centre SFB1120-236616214 “Bauteilpräzision durch Beherrschung von Schmelze und Erstarrung in Produktionsprozessen” and funded by the Deutsche Forschungsgemeinschaft e.V. (DFG, German Research Foundation). We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at PETRA III and we would like to thank F. Beckmann and J. Moosmann for assistance in using P07 EH4. Beamtime was allocated for proposal I-20191140.The sponsorship and support is gratefully acknowledged.