The effect of high temperature, high strain rate deformation on the evolution of second phase particles in commercial aluminium alloys has been investigated. Three model alloys provided by Novelis have been examined, and the evolution of particles during deformation has been examined for the alloy that most closely resembles the composition of alloys used in commercial applications. The effect of deformation mechanisms was expected to be an enhancement of diffusion controlled processes; therefore the first part of the work was to develop a heat treatment that would produce a fine distribution of dispersoid particles. This heat treatment was then used to prepare material for torsion testing, at strain rates similar to those found during the hot rolling stage of commercial production. Testing was performed at both the end of heat treatment temperature, to remove thermal effects, and at a lower temperature which more closely represents the temperature during commercial rolling. Material was examined by optical microscopy, FEGSEM and TEM and the particle populations were characterised by backscattered FEGSEM imaging and image analysis. This demonstrated that the disperoid particle population develops in multiple ways. Along with the enhancement of coarsening there is a significant shape change to the dispersoid particles, suggesting a change in the character of their interface. It has also been demonstrated that there is nucleation of new particles, despite a long prior hold time, in material deformed at the same temperature as the heat treatment. Material deformed at lower temperatures also demonstrated a larger increase in the volume fraction of dispersoid than material with the same thermal history. A constitutive model for diffusion enhancement and a model for particle evolution have been combined to simulate the effects of thermomechanical processing on the particle population.
|Date of Award||31 Dec 2015|
- The University of Manchester
|Supervisor||Joseph Robson (Supervisor)|
- Hot Rolling