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During the homogenisation process of Al-Mg-Si extrusion alloys, plate-like -Al 5 FeSi particles transform to multiple roundedAl 12 (FeMn) 3 Si particles. The rate of this to transformation determines the time which is required to homogenise the aluminium sufficiently for extrusion. In this paper, a finite element approach is presented which model the development of fraction transformed with time, in the beginning of the transformation, as a function of homogenisation temperature, as-cast microstructure and concentration of alloying elements. We treat the to transformation mathematically as a Stefan problem, where the concentration and the position of the moving boundaries of the and particles are determined. For the boundary conditions of the model thermodynamic calculations are used (Thermo-Calc). The influence of several process parameters on the modelled transformed fraction, such as the temperature and initial thickness of the plates, are investigated. Finally the model is validated with experimental data.

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