Lightweight constructions in the field of traffic engineering are currently using metallic hybrid structures more than ever, as the legal requirements for CO2 reduction, increasing energy costs and sustainability are becoming more demanding. For this purpose, the joining of steel/non-steel metals is an important aspect. Conventional welding processes, like resistance spot welding or friction stir welding, are not well suited in metallurgical as well as technological and economic terms. In this respect, magnetic pulse welding represents a suitable process with low cycle times for producing steel/aluminum hybrid joints with low thermal deformation and without temperature-induced microstructural changes. For widespread industrial use of magnetic pulse welding, detailed knowledge regarding fatigue behavior and the associated damage mechanisms is needed.
In this study, magnetic pulse welded steel/aluminum hybrid joints are investigated with the aim of optimizing the process parameters regarding fatigue behavior. Changes in discharge energy, acceleration distance, as well as influences of surface topography and corrosion, are examined regarding fatigue life and damage mechanisms. Instrumented multiple amplitude tests combined with constant amplitude tests are carried out for assessing structure-property-relations in a resource-efficient manner. Physical measuring technologies, i.e., mechanical, electrical, thermal, optical and acoustical sensor technology, are evaluated regarding applicability for the study. Stress-induced change in strain and AC voltage are well suited for reliable detection of damage initiation and estimation of the fatigue limit. Results reveal that the fatigue properties primarily depend on the imperfections of the welding seam, which are affected mostly by the discharge energy and the surface topography. Corrosion shows to be a relevant factor since it decreases fatigue properties. Suitable process parameters are achieved if the fatigue strength of the weld seam lies above the weaker hybrid joint (aluminum). For S235JR and EN AW 1050 (Al99.5) a suitable discharge energy was found to be 15 kJ at an acceleration distance of 1.5 mm.