Microstructures and Hardness Prediction of an Ultrafine-Grained Al-2024 Alloy

High-pressure torsion (HPT) is a high efficiency processing method for fabricating bulk ultrafine-grained metallic materials. This work investigates microstructures and evaluates the corresponding strengthening components in the center of HPT disks, where effective shear strains are very low. An Al-4.63Cu-1.51Mg (wt. %) alloy was processed by HPT for 5 rotations. Non-equilibrium grain and sub-grain boundaries were observed using scanning transmission electron microscopy in the center area of HPT disks. Solute co-cluster segregation at grain boundaries was found by energy dispersive spectrometry. Quantitative analysis of X-ray diffraction patterns showed that the average microstrain, crystalline size, and dislocation density were (1.32 ± 0.07) × 10？3, 61.9 ± 1.4 nm, and (2.58 ± 0.07) × 1014 m？2, respectively. The ultra-high average hardness increment was predicted on multiple mechanisms due to ultra-high dislocation densities, grain refinement, and co-cluster–defect complexes