Effect of Nano-ZrO 2 on the Properties of Al-Al 2 O 3 Nanocomposites Prepared by Mechanical Alloying

In the present work, mechanical alloying was used to prepare Al-20wt.% Al 2 O 3 metal-matrix nanocomposites having up to 4wt.% ZrO 2 at the expense of Al 2 O 3 . The powders were milled for different time intervals. To characterize the powders after milling, x-ray diffraction and transmission electron microscopy were used to identify the phase composition, crystallite size and morphology. In order to study the sinterability, the milled powders were cold pressed and sintered in argon atmosphere at different firing temperatures up to 470 °C for 1 h. The relative density and apparent porosity of the sintered composites were determined according to Archimedes principle. Moreover, the microstructure was examined by a scanning electron microscope attached with an energy dispersive spectrometer (EDS). Microhardness and AC conductivity of sintered composites were also measured. The results pointed out that the increasing of milling time is responsible for uniform distribution of Al 2 O 3 -ZrO 2 particles in the Al matrix as well as remarkable increases in relative density, microhardness and AC conductivity of the sintered specimens. Also, the relative density was affected considerably by the increasing of sintering temperature. Moreover, increasing of ZrO 2 content led to a significant decrease in the crystal size of the milled powders and increase in the microhardness of the sintered compacts. No changes were observed on the conductivity after addition of ZrO 2 .