Atomic-Scale mechanisms of Lithium-Induced grain boundary embrittlement in aluminum alloys: A First-Principles study

This study employs first-principles calculations to investigate the segregation of lithium (Li) at aluminum (Al) grain boundaries (GBs) and its influence on interfacial mechanical properties. Our results reveal that isolated Li atoms interact weakly with most GBs, with binding behavior strongly correlated to the local charge density distribution. As Li concentration increases, distinct clustering behaviors emerge: one-dimensional linear chains form along tilt axes at Σ5(310), Σ17(410), and Σ13(320) GBs, while a stable planar Li monolayer forms exclusively at the Σ5(210) GB. Li segregation weakens interfacial cohesion primarily by inducing localized electron depletion between neighboring Al atoms. The extent of Li segregation and its weakening effect varies across different GB types. Specifically, GBs, such as Σ5(210) and Σ43(335), are highly susceptible to embrittlement due to Li segregation, whereas other GBs, such as Σ3(112) and Σ17(223), show minimal or no effect on interfacial bonding strength. These atomistic insights inform a grain boundary engineering strategy that prioritizes the retention of Li-tolerant GB structures, while suppressing Li-sensitive configurations. This approach offers a roadmap for enhancing fracture resistance in Al-Li alloys without compromising their lightweight advantages.