Graduate School

A-Area Project 1: Phasefield simulation of the solidification of Al-Si

Person in charge: M.Sc. Sebastian Schulz
Motivation and goals:
The eutectic material system aluminium silicon represents one of the most important cast alloys based on aluminium. The solidification behaviour of this binary system and of multicomponent alloys based on it is therefore an important field of research. The phase field method coupled with thermodynamic datasets makes it possible to reproduce the microstructure evolution during solidification by computer simulations. Characteristic variables, as for instance dendrite arm spacings, can be determined from the simulation results and compared to experiments. The goal is to be able to predict the microstructure characteristics dependent on the composition and the process parameters. By this knowledge the process of aluminium casting could be further optimized.
Investigations Results
To execute phasefield simulations, the thermodynamic characteristics of the material system to be simulated must be available. For systems of great economical interest, the thermodynamic properties have been examined by numerous experiments. They are present in the form of thermodynamic data sets. The Gibbs free energies of the individual phases in dependence of the temperature and chemical composition can be computed from these data sets by making use of the Calphad method. These Gibbs free energies and deduced quantities are applied in the simulations in the form of functions, which were fitted for the temperature and concentration range to be examined. By utilizing Calphad data it was possible to reproduce the solidification behaviour of Al-Si. Simulations of equiaxial dendritic growth into an uniformly undercooled melt have been performed. The transition from a planar to a cellular to a dendritic front has been reproduced for the directional solidification of the aluminium rich Fcc phase. Moreover the coupled growth of the silicon rich and the aluminium rich phase has been simulated for an eutectic composition.