"Formability of 7000 aluminum alloys in warm and hot forming condition"
B.-A. Behrens, S. Hübner, H. Vogt (2018); IOP Conference Series: Materials Science and Engineering
Considerations regarding lightweight construction play a central role in the development of new products in the industry. For example, the dynamic behaviour of machine components can be improved by reducing component weights. Furthermore, lightweight construction is at the centre of efforts to reduce greenhouse gas emissions, particularly in the automotive and transportation industries. In the medium and long term, lightweight solutions will also be in demand in the field of electromobility in order to increase the range of vehicles or the permissible payload in the transport sector, among other things. Therefore, the Institute of Forming Technology and Machines Hanover investigates the processing of new ultrahigh-strength materials and material systems and develops process routes to further exploit the lightweight potential of conventional materials.
One topic here is the forming processing of fibre-reinforced plastic composites. By using thermoplastics as a matrix material, it is possible to use conventional forming presses and peripherals and to reduce the cycle time for manufacturing components. In particular, the production of hybrid components made of FRP and metallic components is the focus of research at IFUM. In various projects, the joint forming of steel with FRP could be realised and a composite of both materials could be produced. This supports and advances the production of components that are specially adapted to local loads and thus save weight.
Another field of research is the form hardening of steels. This process, which is already industrial established, is being investigated in greater detail at the IFUM with regard to exploiting its lightweight construction potential. Novel processes are being developed in the area of tailored tempering, which allow the load-adapted production of components from a monolithic semi-finished product. In particular, the focus is on process time reduction. On the one hand, in the heating of the blanks by conductive austenitizing processes. On the other hand, also through the use of peripheral cooling systems, which relocate the cooling of the components away from the press area and thus increase the productivity of the systems. Similarly, the lightweight potential of hot-stamped components can be increased by using new steel materials. The adjustments required to the heating, forming and trimming processes are also the subject of research projects at the IFUM.
In addition to the forming of high-strength and ultra-high-strength steel materials, lightweight solutions are achieved in particular through the use of non-ferrous materials such as aluminium and magnesium. However, these can usually only be formed to a limited extent and therefore require adapted processes. Investigating the forming potential of such materials is therefore a central aspect of research. Among other things, processes of warm and hot forming are investigated for various materials. One major field of research is the investigation of ultra-high-strength aluminium alloys. These offer a high potential for lightweight constructions.
PUBLICATION
In recent years, the automobile industry has been calling for new lightweight solutions to fulfill increasing ecologically requirements. A weight reduction of automobile body constructions is necessary to reduce fuel consumption and CO2 emissions. In order to reach this aim, new materials and novel forming processes are required. Also, the importance of aluminum alloys in the automobile industry is constantly increasing. Nowadays, mainly alloys of the 5000 and 6000 aluminum series are used for structure parts or shell parts, respectively. Another alloy series are the 7000 aluminum materials. These alloys offer a great lightweight potential due to their high specific strength combined with a moderate ultimate elongation. Nevertheless, these alloys are not yet widely used in the automobile industry. The reason is the limited formability of 7000 aluminum at room temperature in high-strength heat treatment condition. There are two approaches to increase the formability based on elevated temperatures, specifically the two processes of warm and hot forming at temperatures lower than the recrystallization temperature or above it, respectively. This paper deals with the investigation of the influence of forming conditions, especially the forming temperature. Trapezoidal parts were deep-drawn at different forming temperatures and subsequently investigated by determining the deformation with an optical measurement system as well as the springback of the material. In addition, the influence of the forming temperature on the flange feed was investigated as well as the influence of the paint bake process on the artificial aging step. Results show, that the formability increases with increasing forming temperature in the warm forming process route. Also, the artificial aging time can be decreased by a combined aging with paint bake heat treatment.
