Precipitation in a high silicon Al–Si alloy studied by isothermal calorimetry

The precipitation in an Al–6mass%Si alloy was investigated by isothermal calorimetry. Three types of heat treatment were studied and precipitation rates in the samples increase in the order: Furnace cooled, ice-water quenched (IWQ) and naturally aged after IWQ. With the aid of a novel model for nucleation and growth reactions the measured exothermic heat flow is interpreted in terms of two processes: Growth of large undissolved Si particles and growth of pre-existing nuclei. The activation energies for precipitation are EA=0.89 eV for IWQ samples and EA=0.94 eV for furnace cooled samples.