UBC Theses and Dissertations
Modelling the interaction between recovery, recrystallization and precipitation in AA6111 Go, Johnson
The present work investigates the evolution of microstructure during the annealing of an industrial precipitation hardened aluminum alloy AA6111. Special emphasis is placed on understanding the interaction between recovery, recrystallization and precipitation through a combination of experimental and modelling approaches. Experimentally, extensive heat treatments were carried out to study the effect of varying initial precipitate conditions on the isothermal annealing behaviour of the alloy in the temperature range of 250-445°C. A total of four prior aging conditions were considered: naturally aged (T4), peak aged (PA), overaged (OA) and severely overaged (SOA). It was found that recrystallization was severely retarded at the annealing temperature of 325°C irrespective of prior precipitate conditions. Microscopic evidence confirmed that the growth of recrystallizing grains is directly related to the non-uniform spatial distribution of precipitates. Subsequently, a new microstructure model was developed to link the changes in the microstructure to the mechanical properties of the alloys. The model which was developed based on the internal state variable approach is capable of translating quantitatively the interaction between recovery, subgrain growth, recrystallization and precipitation into a yield stress vs. time relationship. The effect of non-uniform distribution of precipitates was considered explicitly by using a simple rule of mixtures. The validity of the model was verified by comparing the model calculations to the experimental data obtained from overaged 40% cold rolled AA6111.
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