Multi-metal-design is increasingly gaining importance with regard to lightweight design for enhancement of dynamic range, resource optimization and emission reduction in many fields of traffic engineering in order to achieve the targets of energy efficiency. Conventional welding processes, as for example resistance spot welding or friction stir welding are not well suited for multi-metal-design in metallurgical terms as well as from a technological and economic view. Instead, magnetic pulse welding offers the opportunity to produce hybrid joints of steel and aluminum with a low amount of thermal distortion and without temperature-induced microstructural changes. Low cycle times combine these benefits with a high productivity. However, the lack of knowledge about the fatigue behavior and damage mechanisms inhibit a wide-scale use of magnetic pulse welding.
The aim of this study is to optimize the process window for magnetic pulse welding in terms of fatigue properties of hybrid joints of S235JR and EN AW-1050 (Al99.5). Therefore, the focus lies on a resource-efficient determination of the influence of process parameters, i.e. the discharge energy (9-15 kJ) and the acceleration distance (1-2 mm), on the fatigue behavior and damage mechanisms. The structure-property-relations were evaluated by means of combined instrumented load increase and constant amplitude tests. The experimental procedure was developed by application of different physical measuring technologies, i.e. mechanical, electrical, thermal, optical and acoustical sensor technology. The results show that the plastic strain amplitude and change in AC voltage are well suited for reliable detection of damage initiation and estimation of the fatigue limit. It can be concluded that the fatigue properties are mainly determined by imperfections of the welding seam which is directly influenced by the process parameters. For optimal process parameters, the fatigue strength is determined by failure of the weaker aluminum.