  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.
