Microstructural evolution , strengthening and thermal stability of an ultrafine - grained Al - Cu - Mg alloy

To gain insight into the origin of the ultra-high strength of ultrafine-grained (UFG) alloys, the solute clustering, precipitation phenomena, and microstructural evolutions were studied in an UFG Al-4.63Cu-1.51Mg (wt.%) alloy (AA2024) processed by high-pressure torsion (HPT). The thermal analysis was performed using differential scanning calorimetry. The microstructures, internal microstrains and hardness following heating at a constant rate were characterised at room temperature using Xray diffraction (XRD), transmission electron microscopy (TEM) and atom probe tomography (APT). The microhardness of the HPT processed sample initially increases following heating to 140 °C, and then remains unchanged on further heating to 210°C. As the temperature increases up to 210 °C, the crystallite size calculated from XRD line broadening remains about 60~70 nm, while the dislocation densities remain in excess of 2×10 m. A multimechanistic model is established to describe the strengthening due to grain refinement, dislocation accumulation, solid