Improvement of the high strain rate superplasticity of aluminum materials by equal channel angular pressing of sheet metals

本项目继续的目的仍然是利用等通道角压（ECAP）技术提高铝板超塑性成形（SPF）的可能成形速度，同时降低温度。对于两个项目合作伙伴来说，会出现额外的新问题和工作包。成形技术（utg）：研究项目的结果表明，用现有的ECAP工具可以成形铝板材料。然而，与传统的ECAP相比，样品厚度和通道几何形状之间的比例导致金属板ECAP的剪切变形较小。如果通道的几何形状被改变为有利于这个比率，并且通道半径减小，则会出现明显的薄片厚度不均匀性和内角半径处的裂缝。这些问题应该通过施加反压力来减轻。在数值研究的基础上，已经可以证实这种措施对板材是有效的。通过实施反压，实验室方法ECAP的工业适用性迈出了重要的一步。因此，从生产工程的角度提出了以下问题：•如何在板材的ecap工具中实施反压，以进一步增加引入的剪切应变？•如何选择这种反压和相应的通道配置，以实现无裂纹表面和板材材料中最均匀的应变分布？材料科学（LWW）：在项目范围内，eca加工的金属板的热处理对可实现的应变的显著影响已经显示出来。这是由于形成的微观结构具有热稳定性。借助特定的恢复或再结晶热处理，可以调整具有不同热稳定性的组织，并研究其对超塑性成形工艺的适用性。因此，重点是在不同的ecap后热处理后塑性变形过程中获得微观结构机制的基本理解。不同的微观结构将被调整，通过（透射）电子显微镜方法检查，随后它们在不同温度和应变速率下的变形行为将在拉伸试验中表征。从材料科学的角度来看，出现了以下问题，这些问题的答案将对项目的整体成功做出重大贡献：•热处理后的哪些微观结构过程会影响可实现的（超）塑性应变？•UFG微观结构的热稳定性有什么影响？动态再结晶在多大程度上改变了热成形过程中的应变值？

The aim of this project continuation is still to increase the possible forming speed while simultaneously reducing the temperature for superplastic forming (SPF) of aluminum sheets by using Equal-channel Angular Pressing (ECAP). For both project partners, additional new questions and work packages arise. Forming technology (utg):The results of the research project have shown that forming of aluminium sheet materials is possible with the existing ECAP tool. However, the proportions between sample thickness and channel geometry cause lower shear deformations in the ECAP of sheet metal than in conventional ECAP. If the channel geometry is changed in favour of this ratio and the channel radii are reduced, significant inhomogeneities over the sheet thickness and cracks at the inner corner radius occur. These problems should be reduced by applying a counterpressure. On the basis of numerical investigations, this measure can already be confirmed as effective for sheet materials. By implementing a counterpressure, a significant step towards the industrial applicability of the laboratory method ECAP can be taken. The listed questions consequently arise from a production engineering perspective:• How is a counterpressure implemented in the ECAP-tool for sheet materials in order to further increase the shear strains introduced?• How must this counterpressure and the corresponding channel configuration be selected in order to achieve a crack-free surface and a most homogeneous strain distribution in the sheet material? Materials Science (LWW):Within the scope of the project, a pronounced influence of a heat treatment of the ECA-processed sheet metal on the achievable strains has been shown. This is due to the thermal stability of the formed microstructure. With the help of specific recovery or recrystallisation heat treatments, microstructures with different thermal stability can be adjusted and their suitability for superplastic forming processes can be investigated. The focus is therefore on obtaining a fundamental understanding of the microstructural mechanisms during plastic deformation after different post-ECAP heat treatments. Different microstructures will be adjusted, examined by (transmission) electron microscopic methods and subsequently their deformation behaviour at different temperatures and strain rates will be characterised in tensile tests. From a materials science point of view, the following questions arise, the answers to which will contribute significantly to the overall success of the project: • Which microstructural processes during post heat treatment influence the achievable (super)plastic strain?• What influence does the thermal stability of the UFG microstructure have and to what extent does dynamic recrystallization change the strain values during hot forming?