Nucleation Kinetics of the γ-Phase in a Binary Mg-Al Alloy

The binary magnesium-aluminum system has been studied extensively the last decades. Surprisingly, the kinetics of nucleation of the γ-precipitates (Mg₁₇Al₁₂) in the α-matrix have not been determined experimentally in detail. The main goal of this research is to investigate the precipitation kinetics of the γ-phase in a Mg-Al alloy during annealing, and to understand the relation between the precipitate volume fraction and the mechanical properties of the material. Comprehensive micro-structural analysis was undertaken to reveal the number density, volume fraction, and morphological changes of the γ-precipitates after solution heat treatment (homogenization) and during subsequent annealing below the solvus temperature. As a result, the incubation time and steady state nucleation rate of γ-precipitates in the α-matrix were determined by fitting the experimental data to the classical nucleation theory.