Ab initio investigation on the effect of solid solution RE on interface and mechanical properties of Al–Mg–Si alloy

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Investigating the role of solid-solution rare earth elements (REs) in Al–Mg–Si alloys helps to gain a deeper understanding of the mechanisms of solid-solution elements, enabling the adjustment of alloy composition to improve the microstructure and overall performance of the alloy. This study employs first-principles computational methods to reveal the impact of rare earth element addition on the interface properties of α-Al/β″–Mg5Si6 and α-Al/β–Mg2Si in Al–Mg–Si alloys, as well as the effects on the mechanical properties of β″ and β precipitate phases. The study first constructs two interface models, Al(130)/Mg5Si6(100) and Al(001)/Mg2Si(001), to analyze their interface properties. Based on this, the substitution positions of rare earth elements in the interface models after their addition are further discussed. The results indicate that the atomic substitution positions of rare earth elements are related to crystal structure, interface properties, rare earth atomic radius, and electronegativity. Interface property studies show that the addition of rare earth elements significantly enhances the adhesion of Al(130)/Mg5Si6(100) and Al(001)/Mg2Si(001) interfaces, reduces interface energy, and strengthens interface stability. Additionally, the effects of rare earth element addition on the lattice mismatch of Al(130)/Mg5Si6(100) and Al(001)/Mg2Si(001) interfaces exhibit opposite trends and, to some extent, inhibit the β″ → β phase transformation. Mechanical property studies of the precipitate phases reveal that rare earth atoms in solid solution in β″ and β phases decrease the bulk modulus, shear modulus, and Young modulus, while increasing the Poisson ratio and B/G ratio. This indicates that the introduction of solid-solution rare earth elements reduces the alloy's stiffness and shear resistance while enhancing its plasticity and brittleness.