The effects of increasing the SiC particles volume fraction on the microstructure and elemental diffusion of Al-4.5 wt.%Cu/SiCp nanocomposites synthesized via mechanical milling (MM) process were evaluated in the current work. X-ray diffraction (XRD) technique, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) were utilized to evaluate the structure and elemental diffusion of the milled powders. Results revealed that increasing the SiC particles volume fraction gives rise to an increase in micro-strain, lattice parameter and a decrease in crystallite size. Furthermore, the size of most SiC particles after 5 h milling time at the ball-to-powder weight ratio (BPR) 20:1 was less than 100 nm for Al-4.5%Cu/4 vol.%SiC. On the other hand, detection of AlCu3, Al2Cu3, and AlCu phases after aging process indicates the fact that a supersaturated solution of copper in aluminum was formed during MM process. (c) 2012 Elsevier B.V. All rights reserved.