Precipitation in Al–Mg–Si Alloys: Modeling

Abstract

Different approaches for modeling of precipitation in Al–Mg–Si alloys are reviewed. First of all, the importance of a precipitation modeling and its interrelations with other components in a process model are explained. Then the empirical, statistical, and physically based modeling, with each being a different modeling approach, are introduced. The Kampmann–Wagner numerical (KWN) model, which is a physically based finite difference method, is explained as a model that is able to capture simultaneous nucleation, growth, and coarsening reactions. The growth kinetics in the KWN model is based on the assumption of local equilibrium hypothesis, inferring that there is an immediate thermodynamic equilibrium as soon as two phases are in contact. This assumption implies the diffusion-controlled nature of the transformation. The other extreme approach is the assumption of interface-controlled growth, where the interface reaction (atom transport across the interface) controls the kinetics. In reality, neither of these scenarios can be absolutely true. A modified version of KWN model such that the growth can be treated with a mixed-mode nature (neither pure diffusion-controlled nor pure interface-controlled) is introduced. How the geometry of precipitates can be incorporated into the precipitation model is also explained.