Solute segregation on structural defects in an ultrafine-grained Al-Cu-Mg alloy

Microstructure evolution of an ultrafine-grained Al-Cu-Mg alloy has been studied during and after high-pressure torsion (HPT) at ambient temperature. Hardness distribution in aluminum disks is characterized by micro-Vickers hardness. The ultrafine-grained microstructures after HPT are examined by transmission electron microscopy (TEM), X-ray diffraction and differential scanning calorimetry (DSC). The location, structure and composition of clusters and nanoscale precipitates along lattice defects (dislocations, cell walls or grain boundaries) are clarified by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The microstructure observation reveals grain refinement and dislocations contribute to a significant increase in hardness. Differential scanning calorimetry (DSC) is used to analyze the energy absorption during this stage of hardening. It is found that, during during the DSC after HPT work hardening, a substantial exothermic heat evolution occurs. The source of reaction enthalpy involves dislocation annihilation, the growth of ultrafine grains and grain boundary segregation