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 degrees 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 GPB(1) 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 theta' 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. (C) 2018 Elsevier B.V. All rights reserved.