Regarding the legal requirements for the emission of pollutants from vehicles, the reduction of moving masses and the resulting fuel savings represent an important goal. Lightweight struc-tures made of high-strength steels and light metals like aluminum alloys, which are particularly used in multi-material car bodies, offer great potential for a sustainable weight reduction. In addition to suitable substitution materials, joining processes play a key role, as highly resilient and age-resistant joints must be created between dissimilar materials. The aluminum alloys and steels predominantly used in car body concepts exhibit, among other properties, large differ-ences in their melting temperatures. Therefore, they can only be joined to a limited extent by established resistance spot welding or other conventional fusion welding processes. Ultrasonic metal welding is a suitable alternative due its solid state processing. It is also characterized by high energy efficiency and the absence of additional components and filler materials.

Within the scope of a research project at the Department of Sustainable Systems Engineering (INATECH) of the University of Freiburg ultrasonic metal welding of the aluminum wrought alloy EN AW-6005A-T4 with the galvanized dual phase steel HCT980X is investigated. The focus is on the arrangement and sequence of several welding spots as well as their interaction in terms of oscillation in order to fundamentally examine near-component structures. The ef-fects of additional clamping elements on the joining process are determined and related to the oscillation propagation in the sheets. Both the welding process and the joints are examined and evaluated. The influence of the corrosion-protective zinc layer of the steel sheets on the properties and failure behavior of the multi-spot-joints are studied based on fractography after mechanical loading.