Untersuchungen zur Stoffflusssteuerung beim Fügen durch Umformen von hochfesten Aluminiumlegierungen mittels lokaler Kurzzeitwärmebehandlung

Description

Mechanical joining processes take an important role in the production of multi-material car bodies. Due to the high strength and usually limited formability of modern high-performance materials, established joining processes are reaching their limits. This applies in particular to the joining of high-strength 7xxx alloys. Heat treatment can be used to adapt the properties of precipitation-hardenable alloys in order to improve their forming characteristics. If the heat treatment is locally limited, the material flow in forming processes can be controlled by the interaction of softened and not-softened areas. The aim of the present work was to fundamentally investigate the control of the material flow during joining by forming of 7xxx aluminum by means of a process-adapted, locally limited short-term heat treatment and to derive a comprehensive understanding of the process. For this purpose, the influence of short-time retrogression annealing of EN AW-7075 T6 aluminum alloy on its mechanical properties was deter-mined, and the process limits when joining the alloy by shear-clinching with die-sided 22MnB5 and HCT780X were identified. By varying the heat treatment parameters, circular and ring-shaped layouts were compared and their influence on the joining process and the joint properties were investigated. Since the material re-ages after retrogression, the work further focusses on the analysis of the joint properties after artificial ageing as well as on the interaction with the heat treatment preceding the joining process.