Age-hardenable Al–Li alloys are critical lightweight structural materials, offering high specific strength. However, the early-stage decomposition of supersaturated solid solution, specifically formation of Guinier-Preston (GPAl-Li) zones during aging, remains a key gap in understanding precipitation sequence. Using density functional theory and cluster expansion method, we determined effective cluster interactions for Al–Li alloys in an fcc lattice and computed Gibbs free energy via meta-dynamics Monte Carlo simulations. A metastable phase diagram encompassing \({{\rm{\alpha }}}_{{\rm{Al}}}\) , GPAl-Li, and \({{\rm{\delta }}}^{{\prime} }\) phases was constructed across relevant temperatures. GPAl–Li zones was revealed to possess a well-ordered structure, further supported by electronic structure analysis. Kinetic phase-field simulations of early-stage decomposition revealed that within appropriate Li concentration ranges, GPAl-Li zones form rapidly and extensively below 483 K, later transforming into \({{\rm{\delta }}}^{{\prime} }\) precipitates. These GPAl–Li zones should be directly discernable in cryogenic treated Al–Li alloys, owing to their deeper free energy well and sufficiently slow transformation. We propose that even outside this composition range, GPAl–Li zones may form transiently on the path towards \({{\rm{\delta }}}^{{\prime} }\) , justifying their inclusion in precipitation sequence. Factors promoting T1 phase nucleation via GPAl–Li zones in Al–Li–Cu alloys were also explored, providing theoretical insights for advanced alloy design.
