Ab initio analysis of Guinier–Preston–Bagaryatsky zone nucleation in Al–Cu–Mg alloys

Due to the inherit difficulties associated with microstructure characterization in the early stages of aging, the origin of rapid hardening in Al–Cu–Mg alloys remains a poorly understood and controversial issue. This work addresses the precipitation processes in the early stages by ab initio modeling of Guinier–Preston–Bagaryatsky (GPB) zone nucleation. We derive the structural nature of GPB zone nuclei and establish that the nucleation starts with 1D-GPB1 crystals, which represent thermodynamically stable configurations at the size scale previously associated only with solute clusters. It is also established that the 1D-GPB1 can form very rapidly due a simple structural transition from face-centered-cubic-based configurations (clusters). The formation of GPB zones in the early stages of aging is validated by comparison with previous experimental measurements. Based on previous experimental evidence, it is postulated that GPB zones rather than solute clusters may be able to rationalize the rapid hardening in the Al–Cu–Mg alloys.