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

Abstract

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 ⇌ A μ B ν ) has been used to investigate the energetics of formation of intermetallic compound Al 3Mg 2 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 ϕ ij ( r), calculated from pseudopotential theory in the light of CF model. Our study of ϕ ij ( r) suggests that the effective interaction between Al–Al atom in the pure state is found to be smaller than those obtained in Al 0.425Mg 0.575 and Al 0.625Mg 0.375 alloys. Φ Al–Al in the case of Al 0.625Mg 0.375 alloys lies in between pure state (Al) and Al 0.425Mg 0.575 .The nearest neighbour distance does not change appreciably on alloying, whereas the effective interaction between Mg–Mg atoms increase in the order Al 0.625Mg 0.375 < Al 0.425Mg 0.575 < Mg pure, being minimum in CF alloys. The computed values of S M 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 σ 3 and Ψ compound.