Formation of Particle-Dispersed Nanocomposite and Supersaturated Solid Solution by Mechanical Alloying of Al and Al₂O₃ Powders

We investigated the mechanical alloying (MA) processes of Al and Al₂O₃ powders via X-ray diffraction analysis, transmission electron microscopy (TEM), and Vickers microhardness. The yield strengths and microstructures of consolidated compacts were evaluated using tensile tests and TEM, respectively. When the amount of oxygen in the MA atmosphere was higher than a certain threshold, Al₂O₃ particles of about 7 nm were precipitated in the Al grain interior from a supersaturated solid solution (SSS) of Al—O due to significant precipitation driving force. Two types of alloyed powders were obtained: Al₂O₃ particle-dispersed Al nanocomposite and SSS. The consolidated compact of the former exhibited smaller Al grains and higher yield strength than the latter due to the enhancement of the pinning effect on Al grain boundary migration during consolidation. The difference in the nature of the two kinds of powders affected the Al grain sizes and yield strengths of the consolidated compacts.