In commercial thermomechanical processing, metals and alloys are often subjected to complex deformation histories, including changes in the strain rate, temperature and strain path. Due to the complicated nature of the sequences of deformations that thermomechanical processes need to create a final product, the strain path experienced by the majority of volume elements in the material is complicated. However, the relationship between the strain path and the microstructure/texture evolution is not well predicted by current models used in industrial processes. The important properties in metals are sensitive to the anisotropic microstructure of the metal produced via thermomechanical processing. This anisotropy includes crystallographic texture, grain shape, the shape and spatial distribution of particles and deformation induced dislocation boundaries. An understanding of the origin of these microstructural features is, therefore, critical for future improvements in properties. To some extent, under linear deformation conditions the evolutions of parameters are well known. This can not be said, however, for non-linear deformation conditions. In this work the effect of strain path on microstructure and texture evolution of the aluminium alloy AA5052 under hot working conditions has been investigated. Specimens were produced with a wide range of strain paths with many also statically annealed to investigate different stages of recrystallization. The microstructures and textures created in the specimens were then studied using electron backscattered diffraction (EBSD) and the subsequent develop of a program that analyses the recrystallization fraction of the material in function of the crystallographic orientatio. The deformed strain path specimens were created using the Arbitrary Strain Path machine at the University of Sheffield, which is capable of torsion and tension/compression testing. Tests from a single step of torsion through to multiple steps with combined forms of strain, using one, two or more steps of deformation with a value of equivalent strain of 0.25 and small reverse deformation for selected tests of equivalent strain of 0.05. I , , The microstructures formed by the applied deformation and annealing processes were analyzed using EBSD to create profiles that show the behaviour of the microstructures and textures under the different strain paths. More detailed analysis was then carried out using in-house software. The program used quaternion geometry to calculate the mean orientation of each grain and then used the deviation from the mean to analyse the extent of substructure within the grains which enabled the recrystallization fraction for each strain path condition to be calculated. The results show a clear difference between the recrystallization behaviour and the respond of microstructure result of strain path with an equivalent strain of 0.05 of deformation applied on the reverse deformation. The small reverse conditions are quite different showing that applying the small reverse deformation after two steps of forward deformation presents material with significant substructure than just two steps of forward deformation, meanwhile when the small reverse deformation is applied after one step of forward deformation the amount of material with significant substructure decreases. 1I
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:575483 |
| Date | January 2009 |
| Creators | Silva, Oliver Hernandez |
| Publisher | University of Sheffield |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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