Modeling of precipitate free zone in multicomponent aluminum alloys
Résumé
A comprehensive model has been developed for the simulation of microstructure evolution during solidification and homogenization treatments of aluminum alloys. It combines, on the one hand, a pseudo-front tracking method for the prediction of long range diffusion during solidification and homogenization, and, on the other hand, a particle size distribution method for the description of dispersoids. The first method considers the formation of the cellular primary phase (i.e. the fcc aluminum-rich matrix) from the melt and the secondary intercellular phases resulting from eutectic reactions and solid state phase transformations. The second method is applied to the evolution of the precipitates forming within the supersaturated primary cellular phase. Both methods are directly coupled with Thermo-Calc for the calculation of thermodynamic equilibrium. The model is applied to the prediction of microstructure and segregation in a 3003 aluminum alloy for a typical industrial solidification and heat treatment sequence. The influence of the solidification conditions on the prediction of the precipitate free zone is discussed. The simulation results are compared with experimental data collected in the literature for the same alloy and heat treatment conditions. It is shown that controlling the nucleation undercooling of the secondary phases is essential to retrieve the measured volume fractions of intercellular particles and precipitate free zone.