The existing quasi-lattice theory for liquid alloys (QLT), which has been extensively used by many researchers, has been modified by incorporating the knowledge of composition and temperature-dependent coordination numbers. The modified QLT was then used to compute the enthalpy of mixing, the entropy of mixing, concentration fluctuations, Warren-Cowley short range order parameter, surface concentrations and surface tensions of liquid Al-Sn, Al-Zn and Sn-Zn systems, which are the binary sub-systems for Al-Sn-Zn. The effect of the approximation of coordination number in the existing QLT was also investigated and was found to be insignificant when coordination number is 10. This work has provided a more physically realistic quasi-lattice theory, and has contributed to the knowledge on the binary subsystems of Al-Sn-Zn and has also set a foundation for the application of quasi-lattice theory on Al-Sn-Zn and other ternary systems.
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