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

该研究项目的目标是通过在成型前进行定制的局部短期热处理来改善弯曲铝挤压型材的成型极限和最终机械性能的定义调整，从而产生所谓的定制热处理型材（THTP）。在第一个项目期间，研究了6060 T4铝合金的THTP。通过差示扫描量热法（DSC）和一种新开发的用于研究宽范围加热速率的方法，原位表征了由于短期回归退火引起的组织变化。根据加热方法和随后的时效工艺，描述了短期热处理后的机械性能。微观结构变化与机械性能相关，并显示在6060 T4的连续加热溶解图中，包括合适的工艺窗口。对于THTP的成形模拟以及热处理模拟，模型已经由LS-DYNA实现，将来可以耦合到一个集成的过程模型中。弯曲试验台包括一个现场变形测量已经实施，挤压型材已经成功弯曲，并与数值计算结果进行了比较。在第一个项目期间的结果的基础上，新的专题领域已经开发，这将是一个显着的改进THTP的研究。因此，第二个项目期的重点在于一方面加强对短期热处理、微观结构变化和由此产生的机械性能的因果关系的基本理解。另一方面，数值计算的准确性应通过更复杂的材料模型和在短期热处理期间的热机械过程的精确描述来提高。因此，必须考虑铝挤压型材的各向异性性能。此外，短期回归退火后局部不同的冷却速率起着重要作用。具有不同溶解和析出行为的高合金和高强度铝合金6082 T4应纳入调查。此外，数值计算步骤中应考虑沿型材壁厚的温度梯度沿着以及短期热处理的残余应力。最后，应在短期热处理后进行稳定化处理，以保持人工老化潜力。

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.