Unexpected nucleation mechanism of T1 precipitates by Eshelby inclusion with unstable stacking faults

Aluminum-lithium (Al-Li) alloy is one of the most promising lightweight structural materials in the aeronautic and aerospace industries. The key to achieving their excellent mechanical properties lies in tailoring T₁ strengthening precipitates; however, the nucleation of such nanoparticles remains unknown. Combining atomic resolution HAADF-STEM with first-principles calculations based on the density functional theory (DFT), here, we report a counterintuitive nucleation mechanism of the T₁ that evolves from an Eshelby inclusion with unstable stacking faults. This precursor is accelerated by Ag-Mg clusters to reduce the barrier, forming the structural framework. In addition, these Ag-Mg clusters trap the free Cu and Li to prepare the chemical compositions for T₁. Our findings provide a new perspective on the phase transformations of complex precipitates through solute clusters in terms of geometric structure and chemical bonding functions.