Modelling the Metallurgical Reactions during Homogenisation of an AA3103 Alloy

The as cast microstructure of a DC cast AA3103 alloy consists of equiaxed grains with a cellular structure. The periphery of the cells contains high volume fractions of intermetallic phases and there are large variations in the solid solution level across the cells. During a typical homogenisation heat treatment the material is heated at 50 to l00(degrees)C/hour up to a temperature of 500-600(degrees)C and held there for some hours. The material is then cooled to room temperature (extrusion ingot) or fed into the hot-rolling mill (sheet ingot). A model for the metallurgical reactions occurring in this system is constructed based on a cylindrical cell geometry. The as cast microstructure is adopted from a solidification model (Alstruc) that predicts the micro segregation, the volume fraction and the composition of the primary phases. A thermodynamic description of the two phases Al₆(Mn,Fe) and Al₁₅(Mn,Fe)₃Si is proposed, assuming matrix to be a dilute solution and the phases to be regular solutions. Fe and Mn are allowed to Subscriptstitute each other completely. Precipitation, growth and coarsening of the phases are modelled individually in each position across the cell, each particle is designated to a size class and infinite diffusion is assumed inside particles. Diffusion across the cell is accounted for. Model results are compared with measured number density and size distribution of precipitates and electrical conductivity.