First-principles Investigation of Exceptional Coarsening-resistant V-Sc(Al2Cu)4 Nanoprecipitates in Al-Cu-Mg-Ag-Sc Alloys

TL;DR

This study uses first-principles calculations to understand why V-Sc(Al2Cu)4 nanoprecipitates in Al-Cu-Mg-Ag-Sc alloys resist coarsening at high temperatures, revealing their thermodynamic stability and kinetic formation mechanisms.

Contribution

It uncovers the thermodynamic and kinetic factors behind the coarsening resistance of V-Sc(Al2Cu)4 in aluminum alloys, and screens element substitutions to enhance heat resistance.

Findings

V-Sc(Al2Cu)4 is metastable and tends to form a stable ScAl7Cu5 phase.

Kinetic factors govern the temperature-dependent formation of V phase.

Formation of V-Sc(Al2Cu)4 modifies the Omega nano-plate interface, inhibiting thickening.

Abstract

Aluminum-copper-magnesium-sliver (Al-Cu-Mg-Ag) alloys are extensively utilized in aerospace industries due to the formation of Omega nano-plates.However, the rapid coarsening of these nano-plates above 475 K restricts their application at elevated temperatures.When introducing scandium (Sc) to these alloys, the service temperature of the resultant alloys can reach an unprecedented 675 K, attributed to the in situ formation of a coarsening-resistant V-Sc(Al2Cu)4 phase within the Omega nano-plates. However, the fundamental thermodynamic properties and mechanisms behind the remarkable coarsening resistance of V nano-plates remain unexplored.Here, we employ first-principles calculations to investigate the phase stability of V-Sc(Al2Cu)4 phase, the basic kinetic features of V phase formation within Omega nano-plates, and the origins of the extremely high thermal stability of V nano-plates. Our results indicate that V-Sc(Al2Cu)4 is meta-stable and thermodynamically tends to evolve into a stable ScAl7Cu5 phase. We also demonstrate that kinetic factors are mainly responsible for the temperature dependence of V phase formation. Notably, the formation of V-Sc(Al2Cu)4 within Omega nano-plates modifies the Kagome lattice in the shell layer of the Omega nano-plates, inhibiting further thickening of V nano-plates through the thickening pathway of Omega nano-plates. This interface transition leads to the exceptional coarsening resistance of the V nano-plates. Moreover, we also screened 14 promising element substitutions for Sc. These findings are anticipated to accelerate the development of high-performance Al alloys with superior heat resistance.