Modelling of precipitation behavior of Fe in commercial purity aluminum

Abstract

Microstructure and precipitation control for optimizing processing conditions is vitally important for improvement of quality of wrought aluminum alloys. In this study, a model was presented for the precipitation behavior of impurity Fe and Si in commercial purity aluminum. The model was basically constructed under the nucleation and growth theory. The equilibrium stability and solvus temperature of precipitates and equilibrium solvus boundaries of Fe and Si in solid solution were determined by thermodynamic calculation for Al-Fe-Si alloys. The temperature-time-precipitation (TTP) curves for Al 3Fe and α-AlFeSi were mainly described in this paper. In addition, as the effects of strain-induced precipitation, a stored energy term was added to the rate of heterogeneous nucleation, in which the effects of recovery and recrystallization were taken into account. As an experimental verification of this model, the changes in solute Fe contents during isothermal annealing in the undeformed and hot-deformed specimens were quantitatively investigated by chemical analysis of extracted residue with phenol (phenol residue method). The present model quantitatively explained the experimental results, in particular, concerning TTP curves and the accelerated precipitation due to strain.