A COMPREHENSIVE MODEL FOR THE DESCRIPTION OF MICROSTRUCTURE EVOLUTION DURING SOLIDIFICATION AND HOMOGENIZATON OF MULTICOMPONENT ALUMINIUM ALLOYS

摘要

A comprehensive model has been developed for the simulation of microstructure evolution during solidification and homogenization treatments. 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. thence Al-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. The phase equilibrium in the intercellular regions and the driving pressure for precipitation are obtained through a direct coupling with Thermo-Calc. The model is applied to the prediction of microstructure and segregation in an AA3003 alloy for typical industrial solidification and heat treatment sequences. The influence of the solidification conditions and in particular of the nucleation undercooling of the secondary phases 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.