Nanocrystallization of Al Powder by Cryomilling Process

Abstract

Al5083 powder was subjected to ball milling in liquid nitrogen for 8 h using an attrition ball milling. The evolution of morphology of powder particles and the refinement of grain size were studied by scanning and transmission electron microscopies. The results showed that during cryomilling the morphology of powder particles changed from spherical to equiaxed shape. Additionally, the size of powder particles increased from ~10 μm to ~20 μm with narrower distribution. Simultaneously the cryomilling was associated with a significant reduction of grain size so that the final product after 8 h of cryomilling had a nanocrystalline microstructure (~25 nm) with well-developed high angle grain boundaries. These features were discussed in terms of severe plastic deformation, cold-welding and fracturing of powder particles which occur simultaneously during cryomilling process.