A model of the β-AlFeSi to α-Al(FeMn)Si transformation in Al-Mg-Si alloys

Abstract

During the homogenisation process of Al-Mg-Si extrusion alloys, plate-like β-Al5FeSi particles transform to multiple rounded α-Al12(FeMn)3Si particles. The rate of this β to α 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 β to α transformation mathematically as a Stefan problem, where the concentration and the position of the moving boundaries of the α and β particles are determined. For the boundary conditions of the model thermodynamic calculations are used (Thermo-Calc). The influence of several process parameters on the modeled transformed fraction, such as the temperature and initial thickness of the β plates, are investigated. Finally the model is validated with experimental data.