Third party funded individual grant
Start date : 01.10.2025
End date : 30.09.2027
The increasing demands on the automotive industry to reduce the vehicle weight and to increase crash safety at the same time require the extensive use of modern high-performance materials as well as the production of car bodies with a multi-material design. This results in new challenges for joining technologies. This applies in particular to the joining of dissimilar, high-strength materials. Against this background, within the first phase of the project, the focus was to extend the process limits for shear-clinching high-strength aluminum alloys of the 7000 series by means of a tailored short-term heat treatment. The localization of the heat treatment enables the targeted setting of strength gradients in the sheet and thus the influencing of the material flow in the joining process with the aim of improving the properties of the joints. Within the second phase, the findings are to be transferred to joining with auxiliary joining parts. For this purpose, the investigations will be carried out using semi-tubular self-piercing riveting as an example. Furthermore, the control of the cooling rate during the retrogression of precipitation-hardenable aluminum makes it possible to influence the aging behavior and thus the resulting mechanical properties of the alloys. This circumstance is to be used to achieve not only an improvement of the joint geometry by the local heat treatment, but also to influence the resulting application properties by the complete control of the local temperature-time curves. With the aid of numerical simulation, the interaction between the heat treatment layout and the resulting material flow in the semi-tubular punch riveting process is investigated. After cold and artificial aging of the specimens, the resulting application properties are determined by varying the heat treatment layout and the realized cooling rate. In particular, the focus is on the strength under cyclic loading and the susceptibility of the alloy to stress corrosion cracking. It is known from the literature that retrogression followed by re-aging has a beneficial effect on corrosion behavior. The influence of such a heat treatment on the application properties of mechanical joining points is therefore to be analyzed as part of the research project.
The increasing demands on the automotive industry to reduce the vehicle weight and to increase crash safety at the same time require the extensive use of modern high-performance materials as well as the production of car bodies with a multi-material design. This results in new challenges for joining technologies. This applies in particular to the joining of dissimilar, high-strength materials. Against this background, within the first phase of the project, the focus was to extend the process limits for shear-clinching high-strength aluminum alloys of the 7000 series by means of a tailored short-term heat treatment. The localization of the heat treatment enables the targeted setting of strength gradients in the sheet and thus the influencing of the material flow in the joining process with the aim of improving the properties of the joints. Within the second phase, the findings are to be transferred to joining with auxiliary joining parts. For this purpose, the investigations will be carried out using semi-tubular self-piercing riveting as an example. Furthermore, the control of the cooling rate during the retrogression of precipitation-hardenable aluminum makes it possible to influence the aging behavior and thus the resulting mechanical properties of the alloys. This circumstance is to be used to achieve not only an improvement of the joint geometry by the local heat treatment, but also to influence the resulting application properties by the complete control of the local temperature-time curves. With the aid of numerical simulation, the interaction between the heat treatment layout and the resulting material flow in the semi-tubular punch riveting process is investigated. After cold and artificial aging of the specimens, the resulting application properties are determined by varying the heat treatment layout and the realized cooling rate. In particular, the focus is on the strength under cyclic loading and the susceptibility of the alloy to stress corrosion cracking. It is known from the literature that retrogression followed by re-aging has a beneficial effect on corrosion behavior. The influence of such a heat treatment on the application properties of mechanical joining points is therefore to be analyzed as part of the research project.