Surface Tension of Molten Al–Si Alloys Measured by Electromagnetic Levitation: Comparison with Ideal- and Subregular-Solution Calculations

Abstract

Surface tension data for molten Al–Si alloys are important for modeling high-temperature melt-processing phenomena, but the surface tension values in the literature show considerable scatter, particularly with respect to their composition dependence. In this study, surface tension measurements were conducted for pure liquid Al, pure liquid Si, and molten Al–Si alloys containing 5–80 at % Si using the oscillating drop method with electromagnetic levitation. Oxide-affected heating curves were excluded from the pyrometer calibration, and only oscillation data for which no oxide film was observed on the droplet surface were analyzed. For all examined compositions, the measured surface tension decreased linearly with increasing temperature. Near 1700 K, the surface tension decreased monotonically and nearly linearly with increasing Si concentration, and previously reported nonlinear behaviors, such as relatively high values in the Al-rich region and an increase toward the Si-rich side, were not observed. Uncertainty analysis confirmed that the nearly linear composition dependence was not due to measurement uncertainty. Butler equation calculations were performed using the pure-component surface tension values obtained in this study. The ideal-solution approximation reproduced the measured composition dependence and temperature coefficients more consistently than the subregular-solution calculation using the evaluated excess Gibbs energies. These results indicate that thermodynamic nonideality makes only a limited contribution to the surface tension behavior of molten Al–Si alloys under the present experimental conditions.