Interionic pair potential and entropy of mixing of Al–Mg compound forming binary molten alloys

The observed asymmetric behaviour of mixing properties of AlMg liquid alloys around equiatomic composition with smaller negative values for excess free energy of mixing (−0.15 kJ mol−1) has aroused our interest to undertake a theoretical investigation of this system.A simple statistical mechanical theory based on compound formation model (μA + νB ⇌ AμBν) has been used to investigate the energetics of formation of intermetallic compound Al3Mg2 in the melt, through the steady of thermodynamic property such as entropy of mixing.Besides, the interionic interactions between component atoms (Al and Mg) of the alloy have been understood through the study of interionic pair potential ϕij(r), calculated from pseudopotential theory in the light of CF model.Our study of ϕij(r) suggests that the effective interaction between Al–Al atom in the pure state is found to be smaller than those obtained in Al0.425Mg0.575 and Al0.625Mg0.375 alloys. ΦAl–Al in the case of Al0.625Mg0.375 alloys lies in between pure state (Al) and Al0.425Mg0.575 .The nearest neighbour distance does not change appreciably on alloying, whereas the effective interaction between Mg–Mg atoms increase in the order Al0.625Mg0.375 < Al0.425Mg0.575 < Mgpure, being minimum in CF alloys. The computed values of SM from pseudopotential theory are positive at all concentrations, but the agreement between theory and experimental is not satisfactory. This might be happening due to parameterization of σ3 and Ψ compound.