Mg₁₇Al₁₂ phase precipitation kinetics in die casting alloys AZ91D and AM60B

The major second phase in magnesium die casting alloys containing aluminum (i.e., AZ91D and AM60B) is Mg₁₇Al₁₂, termed β-phase in the magnesium literature. In this study, in-situ high temperature x-ray diffraction was used to study the precipitation of this phase from the as-cast matrix. It is indicated that appreciable precipitation of this phase will occur during service at elevated temperatures. Experimental data for the instantaneous volume fraction of β-phase were fit to an adapted Avrami equation. The obtained fit parameters may be used to predict the amount of precipitation that will occur under given service of aging conditions. The impact upon elevated temperature mechanical behavior is also discussed.