Uncovering the Interfacial Strengthening Mechanisms of α-Mg/Mg₂Sn/β-Li Interfaces Using First-Principle Calculations...

Area of Science:

• Materials Science
• Metallurgy
• Computational Materials Science

Background:

• Previously reported ultralight Mg-Li-Al-Zn-Mn-Gd-Y-Sn (LAZWMVT) alloy with high modulus.
• Observed significant strength and stiffness increases with minor tin (Sn) additions.

Purpose of the Study:

• Investigate the mechanism by which Mg2Sn enhances interfacial bonding in Mg-Li alloys.
• Explore the role of Mg2Sn as an interfacial binder between α-Mg and β-Li phases.
• Determine the contribution of Mg2Sn to the overall mechanical properties and stability of the alloy.

Main Methods:

• First-principle calculations to model interfacial structures and bonding.
• High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) experiments.
• Analysis of interfacial structural models, formation enthalpy, cleavage energy, and critical cleavage stress.
• Interfacial electronic structure and crystal orbital Hamiltonian population analysis.

Main Results:

• Mg2Sn forms stable ternary composite structures (α-Mg/Mg2Sn/β-Li) with favorable formation enthalpy (-1.95 eV/atom).
• Mg2Sn significantly enhances interfacial bond strength, with bond strengths of Mg2Sn interfaces exceeding that of the β-Li/α-Mg phase.
• Electronic structure analysis reveals denser charge distribution and larger charge transfer at Mg2Sn interfaces, forming stronger chemical bonds.
• Mg-Sn covalent bonds (2.61 eV) are substantially stronger than Mg-Li bonds (0.39 eV), primarily due to Mg 3p-Sn 5p orbital interactions.

Conclusions:

• Mg2Sn acts as a vital interfacial binder, strengthening the α-Mg/β-Li interface in Mg-Li-Al-Zn-Mn-Gd-Y-Sn alloys.
• The enhanced mechanical properties are attributed to the formation of robust Mg-Sn covalent bonds facilitated by Mg2Sn.
• This understanding provides a pathway for designing advanced lightweight alloys with superior strength and stability.