Structural evolution during mechanical milling of nanometric and micrometric Al2O3 reinforced Al matrix composites

The morphological and microstructural changes during mechanical milling of Al powder mixed with 5 vol% nanoscaled alumina particles (35 nm) were studied. The milling was performed in a planetary ball mill under argon atmosphere for various times up to 24 h. The process was also conducted for Al and Al–5 vol% Al2O3 (1 μm) powders to explore the role of reinforcement nanoparticles on the mechanical milling stages. The results showed that the addition of hard particles accelerate the milling process, leading to faster work hardening rate and fracture of the aluminum matrix. Meanwhile, the structural evolution during mechanical milling of the microcomposite powder occurred faster than that of the nanocomposite powder. The result of X-ray diffraction analysis by Williamson–Hall method determined that the so-called crystallite size and lattice strain of the Al matrix of nanocomposite are smaller than that of the microcomposite. Meantime, the particle size distribution and bulk powder density of the two composites were found to be rather equal after 20 h milling, but they were significantly different from those of the unreinforced Al. The mechanisms of mechanical milling for the reinforced and unreinforced Al powders are addressed with stressing on the role of alumina particles.