Thermodynamics of ultra-thin oxide overgrowths on Al–Mg alloys: Role of interface energy

•Formalism was developed to predict ultra-thin oxide overgrowth on Al–Mg substrate.•Interface energies along with bulk Gibbs free energy were included in formulation.•Lower interface energies are found to stabilize amorphous Al2O3 at low thicknesses.•Larger bulk Gibbs free energies stabilize crystalline MgO at higher thicknesses.•Model predictions are in agreement with experimental observations.

A thermodynamic model is developed to predict the ultra-thin crystalline oxide overgrowth due to dry, thermal oxidation of single crystalline 〈AlMg〉〈AlMg〉 alloy substrate with respect to various parameters. Along with the bulk Gibbs free energies, this model also took the alloy/oxide interface energies and oxide surface energies into consideration. The developed model was then compared with the amorphous oxide overgrowths on this alloy substrate. For all cases, stability of a particular oxide at lower oxide-film thicknesses is found to be due to its lower interface and surface energies. The model predictions are found to be at par with the experimental observations.

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