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

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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?