  An age-hardenable Al-Cu-Mg alloy (A2024) was processed by high-pressure
torsion (HPT) for producing an ultrafine-grained structure. The alloy was
further aged for extra strengthening. The tensile strength then reached a value
as high as ~1 GPa. The microstructures were analyzed by transmission electron
microscopy and atom probe tomography. The mechanism for the high strength was
clarified in terms of solid-solution hardening, cluster hardening, work
hardening, dispersion hardening and grain boundary hardening. It is shown that
the segregation of solute atoms at grain boundaries including subgrain
boundaries plays a significant role for the enhancement of the tensile
strength.
