Microstructure and texture evolution upon cryogenic forming of aluminum alloysWednesday (06.11.2019) 16:40 - 17:00 Part of:
Against the trend of increasing the formability of aluminum alloys by raising the forming temperature, a deformation at cryogenic temperature already strongly enhances the uniform elongation. Pure Aluminum and the two standard Aluminum alloys EN AW-5182 and EN AW-6016 have been tested at -196 °C (liquid nitrogen). In all materials, the increase of strain hardening positively influences the formability. Moreover, the suppression of the Portevin-Le Chatelier effect in AlMg alloys is a well-accepted explanation for the higher reachable strains.
As it strongly effects the final forming properties, the microstructure and texture evolution upon deformation at liquid nitrogen as well as room temperature was studied by electron backscatter diffraction (EBSD). When comparing the samples after tensile tests at the different testing temperatures, the main difference lies in the intensity of the new formed texture components, which are in most cases stronger in the samples tested at room temperature. EBSD analyses also allowed to detect local and orientation dependent changes in misorientations, emerging slip traces and sub structures as well as grain-interactions, caused by the tensile deformation. Besides the testing conditions, the deformation structure and texture are also strongly affected by the alloy composition.
In order to further study the differences in the materials behavior during tensile testing at liquid nitrogen and room temperature, in-situ high energy X-ray diffraction experiments connected with X-ray line profile analyses were performed. By means of this method a change in the dislocation character with temperature could be identified and directly correlated to the sample temperature and the applied tensile strain.