•Ultrasonically welded ageing resistant Al/CFRP-joints with ultimate lap shear forces of up to 8300 N.•Insulating character by glass fiber surface ply of all hybrid joints proven.•A metallographic characterization of the joining zone shows adhesive (between aluminium and polymer) as well as cohesive (between aluminium and glass fibers) components of bonding.•Analysis of bond formation with the aid of process data recording. Ultrasonic metal welding is a promising process for joining light metals with fiber-reinforced thermoplastics. The technique is characterized by high reproducibility, short process times, low energy input, no additional filler materials and finally the possibility of extensive process data logging. With this process, dissimilar aerospace materials are ultrasonically welded and the applied process parameters are optimized by statistical methods. A prediction of ageing resistance is possible by the evaluation of the electrical resistivity of the multi-material-joints. With the help of detailed process parameter recording and microscopic investigations, the bonding mechanism of hybrid AA5024/(GF-)CF-PEEK joints is explained and the kinematics of bonding formation is presented in detail.