X-RAY PEAK BROADENING ANALYSIS OF AA 6061(100-x)-x WT% Al2O3 NANOCOMPOSITE PREPARED BY MECHANICAL ALLOYING

Nanocrystalline AA 6061 alloy reinforced with alumina (0, 4, 8, and 12 wt%) in amorphised state composite powder was synthesised by mechanical alloying and consolidated by the conventional powder metallurgy route. The as-milled and as-sintered (573 K and 673 K) nanocomposites were characterised by XRD and TEM. The peaks corresponding to fine alumina were not observed by XRD patterns due to amorphisation. HRTEM confirmed the presence of amorphised alumina observed in Al lattice fringes. The crystallite size, lattice strain, deformation stress, and strain energy density of the AA 6061 matrix were determined precisely from the first five most intensive reflections of XRD using simple Williamson-Hall models (uniform deformation model, uniform stress deformation model, and uniform energy density deformation model). The uniform energy density deformation model was the best fit and most realistic model for mechanically alloyed powders. This model showed the more anisotropic nature of the ball milled powders. The XRD peaks of as-milled powder samples demonstrated a considerable broadening with percentage of reinforcement due to grain refinement and lattice distortions during same milling time (40 h). The as-sintered (673 K) unreinforced AA 6061 matrix crystallite size from well fitted uniform energy density deformation model was 98 nm. The as-milled and as-sintered (673 K) nanocrystallite matrix sizes for 12 wt% Al2O3 well fitted by the uniform energy density deformation model were 38 nm and 77 nm respectively, indicating that the fine Al2O3 pinned the matrix grain boundary and prevented grain growth during sintering. The lattice parameter of Al matrix in as-milled and as-sintered conditions was also studied.