Effect of nanoscaled reinforcement particles on the structural evolution of aluminium powder during mechanical milling

Abstract

This paper presents experimental results on the synthesis of nanostructured aluminium matrix nanocomposite powders by comilling of nanoscaled SiC and Al₂O₃ particles and micrometric aluminium powder. The effect of the nanometric reinforcement particles on the mechanical milling (MA) process of the soft matrix was studied by scanning electron microscopy, X-ray diffraction (XRD), transmission electron microscopy, laser particle size analyser and standard metallographic techniques. It was found that at the early stage of milling, the nanoparticles are smeared on the surface of the aluminium powder and thus do not significantly contribute in the MA process. As the milling continues, the hard nanoparticles are distributed throughout the matrix and enhance the work hardening rate of the soft material. This leads to premature occurrence of the fracture process, so the steady state condition is attained in a shorter milling time compared with the unreinforced aluminium. It was shown that the structural evolution proceeds faster in Al–nSiC than in Al–nAl₂O₃, which indicates the effect of the reinforcement type on the MA processing of Al matrix nanocomposites. The analysis of XRD patterns of the milled powders also determined a slight difference in the grain refining process of the aluminium matrix during MA dependent on the reinforcement type.