In this study fabrication and characterization of alumina particles reinforced aluminum based metal matrix nanocomposite by mechanical alloying and hot pressing was investigated. Aluminum and zinc oxide powders mixture milled by a planetary ball mill and hot pressing the samples at 400 and 500 ? C under 400 MPa led to fully dense bulk Al-13.4wt%Zn/5vol%Al 2 O 3 nanocomposite. The structural evaluation milled and annealed powders studied by x-ray diffraction, SEM observation and hardness measurement. The aluminum crystallite size estimated with broadening of XRD peaks by Williamson-Hall formula. The results showed that milling of aluminum and zinc-oxide for 60h led to displacement reaction of the zinc-oxide and aluminum to produce Zn and Al 2 O 3 phases. The milled powder had a microstructure consisting of nanosized Al 2 O 3 particles in an Al-Zn solid solution with a nanoscale grain size of 40nm. The zinc oxide was found to be reacted with Al through a rapid self-sustaining combustion reaction process in stoichiometric composition. As a result a zinc matrix composite reinforced by Al 2 O 3 particulate was formed. The results showed that in early stage of milling the solubility limit of Zn in Al is extended compared to equilibrium value. It was also observed that the lattice parameter of the Al matrix in the as-milled powder decreased as a function of the content. However, after longer milling times, decomposition of Zn supersaturated (Al) solid solution appeared to occur leading to an increase of Al lattice parameter. In this state, softening due to the decomposition of the supersaturated solid solution dominates over the work hardening and grain refinement effects reducing the hardness of as-milled powder.
