Heterogeneous nucleation of T1 precipitates in solid solution of Al-Cu-Li alloys from Ag-rich structures: An ab initio study

As the major strengthening phase, T₁ precipitates contribute over 60% of strength to the advanced Al-Cu-Li alloys. Its nucleation is the first critical step in determining how many nanoparticles will make such contributions. Alloying Mg and Ag has been widely used to promote the formation of T₁ precipitates, however, its mechanism remains ambiguous due to the difficulties of imaging solute atoms at the beginning of nucleation. Thanks to the density functional theory (DFT) tools, in this work, we proposed an ζ-like Al₂Ag metastable structure that can efficiently reduce the resistance to dislocation dissociation, in turn promoting the T₁ nucleation. By solving for Ag distribution and interfacial energy within a robust chemical potential window, we have determined that Ag clusters contribute significantly to the early stages of T₁ nucleation. Our work is enlightening for achieving high-strengthening Al-Li alloys by heterogeneous nucleation engineering of T₁ precipitates.