A study of precipitation in the aluminum alloy AA6111

In recent years there has been a renewal of interest in fundamental studies on 6000 series aluminum alloys due to new applications in the automotive and aerospace industries. The work of this thesis focuses on two new approaches to investigating the behaviour of the Al-Mg-Si-Cu alloy, AA6111. First, the temporal evolution of electrical resistivity was measured over a wide range of annealing temperatures (i.e. 200°C to 560°C). From the resistivity data, an approach has been established for extracting the fundamental thermodynamic properties of Q precipitate and, in addition, an estimate of the effect of precipitate spacing on resistivity for a wide range of conditions was developed. Both of these results represent an original approach to relating electrical resistivity measurements to the state of precipitation in the alloy. The second subject of investigation involved applying thermal spikes (of duration 30 to 300 s) in the temperature range of 220-250°C on material either immediately after the solution treatment or following a period of natural aging. It was found that a 60-second spike at 220°C applied to the alloy immediately after solution treatment can inhibit the deterioration of the paint bake response due to natural aging. In general, it was observed that utilizing the thermal spikes immediately after solution treatment provides a better paint bake response than applying the spike after the natural aging period. Finally, the precipitation hardening model of Esmaeili et al. was extended to examine the temperature-time histories of the thermal spikes. In general, it was found that there was good agreement between the model predictions and the experimental results except for the shortest thermal spike experiments.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat