Defective GP-zones and their evolution in an Al-Cu-Mg alloy during high-temperature aging

Nano-precipitates at the two-stage hardening peaks of an Al-5.0Cu-0.4 Mg (wt%) alloy under isothermal aging at 210 °C were thoroughly characterized using aberration-corrected scanning transmission electron microscopy and first-principles energetics calculations. It was observed, for the first time, that individual one-dimensional GPB1 units can form with a high number density in the matrix, due to the stabilization of substitutional defects. The GPII zones at the early-stage peak aging, as well as the θ′ nano-precipitates at the second-stage peak aging, are also frequently found to be defective in structure. Further analyses suggest that the high-temperature age hardening involves a complex association and evolution of the defective GP-zones. [Display omitted] •A high number density of individual GPB1 unit was directly observed in Al alloys.•Most GPB1 units are stabilized by substitutional defects of AlMg and AlCu.•The GPII zones and θ′ precipitates are also frequently defective in structure.•High-temperature age hardening involves complex interaction among the GP-zones.