Solid-liquid phase equilibria in the Al-Fe-Si system at 727 °C

Abstract

Different experimental techniques were combined to acquire better insight into the solid-liquid phase equilibria that tend to be established in the Al-Fe-Si ternary system at 727 °C under a pressure of 1 atm (101,350 Pa). Isothermal diffusion experiments followed by oil quenching were first carried out. The crystal nature, lattice parameters, morphology, and chemical composition of the different solid phases in equilibrium with the liquid were determined by x-ray diffraction, optical microscopy, scanning electron microscopy, and electron probe microanalysis. Points on the liquidus boundary were then positioned both directly by chemical analysis of liquid samples taken from solid-liquid mixtures equilibrated at 727 °C and indirectly by thermal analysis of Al-Si mixtures with controlled iron additions. On the one hand, it has been confirmed in agreement with currently accepted data that the compounds ϑAl13Fe4, αAl7.4Fe2Si (τ5), and δAl3FeSi2 (τ4) are in equilibrium at 727 °C with Al-Fe-Si liquids, the compositions of which have been refined. On the other hand, the authors have shown that the ternary compound γAl3FeSi is in equilibrium at 727 °C with a ternary Al-Fe-Si liquid containing 10.5 to 16.5 at.% Si and 3.2 to 3.5 at. % Fe.