The number of new developed high innovative lightweight materials is increasing steadily nowadays. To use the full potential offered by these materials there is a need for efficient joining technologies, with the capability to realize hybrid structures. Such material compounds, consisting of dissimilar materials are of great interest for research as well as for industry. Conventional joining methods like fusion welding cannot fulfill these high requirements sufficiently. Therefore, innovative joining techniques like the ultrasound enhanced friction stir welding (USE-FSW) were developed and used to realize joints of dissimilar metals. This process combines the low temperature joining method of friction stir welding (FSW) with a superimposed ultrasound introduction and proved its applicability for the combination of aluminum and magnesium. Straß et al. showed the positive influence of ultrasound enhanced friction stir welded Al/Mg-joints by an increased tensile strength of about 25 % and a longer resistance against fatigue by a factor of 3.5. Based on these investigations an extension of the USE-FSW for further combinations such as Al/Steel were implemented. Therefore, the aluminum alloy EN AW-6061 and the steel DC04 were used to realize hybrid joints, which were characterized afterwards to identify their mechanical properties like tensile strength and hardness. Beside destructive tests nondestructive testing like electromagnetic acoustic transducer (EMAT) and X-ray radiography were carried out. Furthermore, microscopic investigations in the form of light-microscopy and scanning electron microscopy (SEM) with EDX-analyses as well as additional corrosion tests, such as Scanning Kelvin Probe (SKP) and electrochemical measurements, were made, to gain a deeper knowledge about the microstructure and the corrosion behavior of these dissimilar metal joints.