The mechanical properties of pure Aluminium, Al-0.2%Cu and Al-0.4%Cu at large strains were studied by channel-die compression at three different temperatures: 77K, 200K and 300K. The results were interpreted in terms of work hardening rate versus stress (0/r) diagrams. The evolution of the structure was studied on a range of scales from macroscopic to microscopic, by optical study of slip lines, X-ray diffraction for texture measurements, Electron Back-Scattering Kikuchi Patterns for local texture measurements, and by Transmission Electron Microscopy for microstructural information. Intense shear banding was observed at large strains in all alloys at all temperatures. The texture evolution was shown to be consistent with this change in deformation mode. At low temperatures, stage HI of deformation was shown to be represented by a straight line in the 6lr diagram. Increasing the temperature lead to a dramatic decrease in work hardening rate and to an increasing concavity of the 0lr plots. The addition of solutes to pure Aluminium was shown to result in an increase of the work hardening rate, which could be represented by a simple translation of the 0/r plots on the stress axis. At large strains, all three materials experienced a stage (stage IV) of constant work hardening at low rate. The stage IV work hardening rate decreased with increasing temperature, and was not influenced by solute content. The stage Ill-Stage IV transition was very sharp at 77K and smoother at higher testing temperatures. Phenomenological models were developed for the prediction of the influence of temperature and solute content on work hardening. Moderate strains were modelled taking into account the evolution of the dislocation density into two different populations during the deformation. The influence of solutes on work hardening was modelled by considering how segregation of solute atoms at the dislocation cores influences dynamic recovery. Stage IV work hardening was considered to arise from the accumulation of dislocation debris resulting from the dynamic recovery events. / Thesis / Master of Engineering (ME)

The present study focuses on the evolving microstructure of Mg alloy AZ31. The material is subjected to channel die compression at room temperature to simulate a reduction stage in the rolling process. Samples are annealed to provoke recovery, static recrystallization, and grain growth. Annealing is carried out at three temperatures for times ranging from 10s to 10,000s. The material’s response is exhibited through the use of data collection methods such as microhardness, optical microscopy, and electron backscatter diffraction (EBSD). Methodology behind experimentation and data collection techniques are documented in detail. Conclusions are made about the effects of the compression and annealing processes on the material’s microstructure. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) model is introduced, and a simple recrystallization kinetics plot is attempted.