Temperature dependent X-ray and neutron diffraction study of the liquid–solid and solid–solid equilibria in the Al 29.2Ga 27Zn 43.8 ternary alloy

Abstract

The Al–Ga–Zn phase diagram has been previously established from calorimetry and X-ray diffraction experiments at variable temperature. In this paper, temperature dependent X-ray and neutron diffraction experiments have been performed to confirm the phase transformations of a specially chosen ternary alloy Al–Ga–Zn, i.e. ZA40–Ga27 or Al 29.2Ga 27Zn 43.8. From X-ray diffraction experiments, the demixing between two ternary solid solutions noted SS α and SS α′, in equilibrium with a liquid phase, has been clearly shown. On the other hand, the neutron scattering experiments have been performed to examine simultaneously the liquid, amorphous and/or crystalline phases which coexist. The coexistence of the solid and liquid phases has been studied from a detailed characterisation of the diffraction background in relation with the evolution of the Bragg peaks intensities. Using this bulk technique, the effect of the cooling rate on the sample microstructure has been clearly shown: both structural disorder and overall texture of the sample are effected. The phenomenon of liquid phase crystallisation on heating which occurs in this ternary alloy {as in the Al–Zn–Sn system [Ph.D. Thesis, University of Toulon-Var, France, 1995; J. Therm. Anal. 52 (1998) 523; J. Therm. Anal. and Cal. 55 (1999) 271]} certainly enhances these microstructural modifications.