Paper PII-11

Treatment of Al-Mg-Si Ternary Phase Diagram by ESTPHAD method

Farkas János, Roósz András

University of Miskolc, Materials Science Institute, Department of Physical Metallurgy

H-3515 Miskolc, Egyetemváros, Hungary

At the simulation of the solidification processes of solid solutions it is necessary to know the data of liquidus and solidus temperatures numerically as well as the so called partition coefficients as function of concentrations. In case of binary alloys it is enough to know the liquidus and solidus curves because concentrations of liquid and solid phases being in equilibrium with each other at the given temperature can be determined from the equilibrium phase diagrams. Thus, the partition coefficient k is known as the quotient of these two concentrations. In case of multicomponent (ternary, quaternary,…) alloys, the partition coefficients cannot be determined from the equilibrium phase diagrams if the processes have more than one degree of freedom (in case of N components, there are N-1 independent partition coefficients), though their knowledge is of basic importance for the simulation of solidification processes.

Therefore, we made a simply method, which is provable with thermodinamics, for estimation of liquidus surfaces and partition coefficients of multicomponent equlibrium phase diagrams. The main task of the method is the polinom whith convinent power, which can describe these parameters concentration depending inside the measured mistake. It was named ESTPHAD from the „Estimation of Phase Diagrams” expression, like CALPHAD. In our present paper we use the Al-Mg-Si ternary phase diagram to show how this method work.

Fig 1. Liquidus temperatures of the Al-Mg-Si ternary system