Flux-free ultrasonic-assisted induction brazing of aluminum-steel joints

• Applicants: Professor Dr.-Ing. Hans Christian Schmale; Dr.-Ing. Lukas Wojarski
• Subject Area: Coating and Surface Technology ; Joining and Separation Technology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 565410803

The flux-free, ultrasonic-assisted induction brazing of aluminum-steel joints is being investigated as part of the research project. Aluminum-steel joints, which are particularly important in lightweight construction, the transport sector, shipbuilding, the rail transport industry and electrical engineering, continue to pose a major challenge for thermal joining technology. In addition to the thermodynamically stable oxide layers, which have to be removed before or during the soldering process, the formation of brittle phases between aluminum and iron also represents an obstacle to widespread industrial application. The aim of the project is therefore to create a sound understanding of the ultrasound-assisted brazing process in the aluminum-steel material system, to use the basic knowledge gained to improve process control and to enable adaptation to other material systems. Within the research project a brazing device will be developed that combines inductive heating with ultrasonic excitation. With the help of this device, experimental investigations will be carried out to systematically analyze the influence of key process parameters such as ultrasonic amplitude, brazing temperature and gap width on microstructure formation and bond strength. At the same time, a coupled simulation model (FEM) will be developed that maps the ultrasonic propagation in the joining partners and the filler material. This model will be utilized in conjunction with experimentally obtained insights to describe the influence of the sound pressure field on oxide layer disruption as well as brittle phase formation. It will derive how ultrasound must be applied to positively influence the connection. The findings from this project include a fundamental understanding of ultrasound's influence on the filler materials as well as its impact on oxide layers and intermetallic phase formation. Furthermore, strategies for targeted process control will be developed to reproducibly manufacture joints with high strength. The combination of experimental results and simulations allows for deriving universally applicable recommendations for industrial implementation of the method. Thus, the project makes a significant contribution to developing sustainable joining processes without using health-hazardous fluxes. The obtained results will be made accessible through open-access publications and freely available simulation models to promote further research.

• DFG Programme: Research Grants