Modeling of precipitate-free zone formed upon homogenization in a multi-component alloy

A comprehensive model is presented for the simulation of microstructure evolution during industrial solidification and homogenization processing of aluminum alloys. The model combines on the one hand micro segregation due to long-range diffusion during solidification and subsequent heat treatment with, on the other hand, precipitation in the primary A1 phase. The thermodynamic data are directly obtained from a CALPHAD (CALculation of PHAse Diagrams) approach to thermodynamic equilibrium in multicomponent systems. The model is applied to the prediction of structure and segregation evolutions in a 3003 aluminum alloy for typical industrial solidification and homogenization sequences. It is shown that: (i) accounting for the nucleation undercooling of the eutectic/peritectic structures solidifying from the melt is essential to retrieval of the measured volume fractions of intergranular precipitates; (ii) calculations of intragranular precipitation ate generally not applicable if long-range diffusion is neglected; (iii) the precipitate-free zone can be quantitatively predicted only based on the coupling between intergranular and intragranular precipitation calculations. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.