Kinetics of isothermal and non-isothermal precipitation in an Al-6 at% Si alloy

A novel theory which describes the progress of a thermally activated reaction under isothermal and linear heating conditions is presented. It incorporates nucleation, growth and impingement and takes account of temperature-dependent solubility. The model generally fits very well to isothermal calorimetry and differential scanning calorimetry data on precipitation in an Al-6 at.% Si alloy. Analysis of the data shows that two processes occur in this precipitation reaction: growth of large Si particles and growth of pre-existing small nuclei. Determination of the sizes of Si precipitates by transmission electron microscopy indicates that interfacial energy contributions are small and have a negligible influence on solubility.