Welding of aluminum-copper joints is an important issue in joining technology for various applications in the energy sector, e.g., battery technology and electronics. Large differences in material properties, such as thermal conductivity, melting and evaporation temperatures, and absorption coefficients, are challenging for industrial applications. However, a fundamental understanding of the phenomena related to joint formation by mixing both materials at the interface is not yet fully understood, i.e., a time-dependent description of the behavior of the keyhole and melt pool, the resulting flow between the two materials, or the corresponding seam defect formation is not yet given.

This paper addresses the analysis of the keyhole and melt pool behavior based on high-speed synchrotron x-ray imaging of aluminum-copper spot welds with recording frequencies up to 100,000 Hz. Advanced image processing enabled a time-dependent visualization of the keyhole and melt pool, as well as quantification of keyhole dynamics based on geometric parameters and Fast Fourier Transformation (FFT) due to the high phase contrast of the synchrotron x-ray imaging. Accompanying simulations of the process based on a multiphase volume of fluid model in Flow 3D provided further information about the flow field at certain time steps to provide a generally valid description of the process dynamics.