Tribological properties of Al6061–Al2O3 nanocomposite prepared by milling and hot pressing

Tribological properties of bulk Al6061–Al2O3 nanocomposite prepared by mechanical milling and hot pressing were investigated. Al6061 chips were milled for 30 h to achieve a homogenous nanostructured powder. A 3 vol.% Al2O3 nanoparticles (∼30 nm) were added to the Al6061 after 15 and 30 h from the beginning of milling. The milling times with Al2O3 in these two samples were then 15 h and 30 min, respectively. Additionally, 3 vol.% Al2O3 (1 μm and 60 μm) was added to the Al6061 after 15 h of milling; where, the micron size Al2O3 in these two samples, was milled 15 h with the matrix. Hot pressing of milled samples was executed at 400 °C under 128 MPa pressure in a uniaxial die. The hot pressed samples were characterized by micro-hardness test, bulk density measurements, pin on disc wear test, and finally scanning electron microscopy observations. Fifteen hour-milled nanocomposite with nanoscale Al2O3, showed improvement in wear resistance and bulk density compared with that of 30 min-milled nanocomposites due to better dispersion of Al2O3 nanoparticles, improved surface quality of nanocomposite particles before pressing and more grain refinement of Al matrix. Moreover, increasing the reinforcement size increased the wear rate because of reduction in relative density, hardness and inter-particle spacing.