Improvement of formability of extruded aluminium profiles by a local short-term heat treatment

• Applicants: Professor Dr.-Ing. Olaf Keßler; Professorin Dr.-Ing. Marion Merklein
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing ; Metallurgical, Thermal and Thermomechanical Treatment of Materials
• Term: from 2013 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 246974870

The objective of the research project is the improvement of forming limits and the defined adjustment of final mechanical properties of bended aluminium extrusion profiles by a tailored local short-term heat treatment before forming, resulting in so called Tailor Heat Treated Profiles (THTP). In the first project period THTP of aluminium alloy 6060 T4 have been investigated.Microstructure changes due to short-term retrogression annealing have been in-situ characterised by differential scanning calorimetry (DSC) and a newly developed method for investigation of a wide range of heating rates. Mechanical properties after short-term heat treatment have been described depending on heating method and subsequent ageing processes. Microstructure changes have been correlated with mechanical properties and displayed in a continuous heating dissolution diagram of 6060 T4 including a suitable process window. For the forming simulation as well as for the heat treatment simulation of THTP, models have been implemented by LS-DYNA, which in future can be coupled into an integrated process model. A test rig for bending including an in-situ deformation measurement has been implemented and extrusion profiles have been successfully bended and characterized in comparison with the numerical results.Based on the results of the first project period new thematic fields have been developed, which shall be researched for a significant improvement of THTP. Thus, the focus of the second project period lies on the one hand on the enhancement of the fundamental understanding of cause-effect relationships regarding short- term heat treatment, microstructure changes and resulting mechanical properties. On the other hand, the accuracy of the numerical calculation shall be improved by more complex material models and a precise description of the thermo-mechanical processes during short-term heat treatment. Therefore, anisotropic properties of aluminium extrusion profiles must be considered. Further, the locally different cooling rates after short-term retrogression annealing play an important role. The high alloyed and high-strength aluminium alloy 6082 T4 with a different dissolution and precipitation behaviour shall be incorporated into the investigations. In addition, temperature gradients along profile wall thickness as well as residual stresses from the short-term heat treatment shall be considered in numerical calculation steps. Finally, a stabilization treatment after short-term heat treatment shall be introduced to preserve the artificial ageing potential.

• DFG Programme: Research Grants