Structural Evolution During Mechanical Milling of Bimodal-Sized Al₂O₃ Particles Reinforced Aluminum Matrix Composite

Hybrid aluminum matrix composite powders reinforced with bimodal-sized Al₂O₃ particles were synthesized by mechanical milling. Two different approaches were investigated for the addition of submicron- and nano-sized Al₂O₃ particles to the aluminum powders. It was observed that the simultaneous addition of bimodal-sized Al₂O₃ particles to the aluminum powders resulted in an equiaxed morphology of the composite powders and the average particle size stabilized after 5 h of milling, indicating that the presence of bimodal-sized particles has greater effect on accelerating milling process as compared to nano-sized particles; the grain size of the aluminum matrix in composite powders was reduced to under 40 nm, approximate to the value obtained in the separate addition case, while a lower rate of refining was observed due to hindrance of submicron-sized particles on the interactions between nano-sized particles and the aluminum matrix.