Dresden 2003 – scientific programme

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M: Metallphysik

M 2: Symposium: Phasenumwandlungen in Schmelzen I

M 2.4: Talk

Monday, March 24, 2003, 11:00–11:15, IFW A

Thermodynamics of phase formation in Al-Si cast alloys with grain-refining alloying elements — •Rainer Schmid-Fetzer, Djordje Mirkovic, and Joachim Gröbner — Technical University of Clausthal, Institute of Metallurgy, Robert-Koch-Str. 42, D-38678 Clausthal-Zellerfeld

The thermodynamics, phase formation and constitution in the technically important systems Al-Si-Ti-B and the alternative system Al-Si-Ce are studied for better understanding of grain refining and solidification.

Calorimetric measurements of the AlB2 enthalpy of decomposition were performed as key experiments. They lead to improvement of the entropy description and the reoptimization of the entire Al-B phase diagram. The improved thermodynamic data are a basis for the extrapolation to the quaternary Al-Si-Ti-B system, from which calculated phase equilibria are shown.

The Al-rich corner and corresponding intermetallic compounds in the Al-Si-Ce system have been experimentally investigated performing DSC measurements as well as XRD and SEM/EDX on equilibrated alloys. Comparison of calculated phase diagram sections to experimental results are presented.

Solidification curves (fraction solid vs. temperature) determined by processing of DSC curves applying a mathematical heat-transfer model are shown, too. The advantages of this approach are highlighted.