Title of the thesis: Material characterization of AA7075-T651 deformed at different temperatures and strain rates
Discussant: Marta-Lena Antti, Division of Materials Science, Luleå University of Technology, Sweden
Supervisor: Lars-Erik Lindgren
Assistant supervisor: Paul Åkerström
Project: European Network for Alloys Behaviour Laws Enhancement (ENABLE) – funded by European Union’s H2020-MSCA-ITN-2017 under the grant agreement No 764979
AA7075-T651 is a precipitate hardened alloy which is used in the structural components in the aerospace, defence and automobile industries. In the licentiate thesis, the mechanical response and microstructure evolution in the alloy during its deformation at varied conditions of strain rate and temperature were discussed.
The mechanical responses of the alloy were studied through compression tests on AA7075-T651 samples using a Gleeble thermo-mechanical simulator and a Split-Hopkinson pressure bar (SHPB) setup at a wide range of temperatures between room temperature and 500 °C. The Gleeble tests were carried out with two comparatively low strain rates of 0.01 and 1 s-1. Whereas the SHPB setup produced high strain rates in the range of 900-2900 s-1.
The microstructure of the samples before and after the compression tests were analyzed using optical microscope (OM) and scanning electron microscope (SEM). Electron back-scattered diffraction (EBSD) technique was employed to study thermally activated mechanisms, such as dynamic recovery (DRV) and dynamic recrystallization (DRX), taking place during hot deformation with 0.01 and 1 s-1 strain rates. Additionally, a deformation path via formation of adiabatic shear bands (ASBs) and cracks leading to the fracture of the material was established in case of high strain rate deformation.
Moreover, the effects of microstructure evolution in the alloy on its mechanical response and vice-versa were analyzed.