Effect of Al₂O₃ content and milling time on microstructure and mechanical properties of aluminum metal matrix composites

In this study, aluminum metal matrix composites (Al-MMCs) reinforced with aluminum oxide (Al₂O₃) (5, 10, 15 wt%) were produced using the powder metallurgy (PM) process. Mixed powders were ball-milled in a vertical high-energy attritor for various durations (1, 2, 3 and 4 h). Milled powders were compacted under 800 MPa pressure to produce standard transverse rupture block specimens of dimensions 6.35 × 12.70 × 31.70 mm. Block specimens were then sintered in a tube furnace at a constant temperature of 650°C for 4 h under argon atmosphere. The hardness and transverse rupture strength of the experimentally produced composites were determined. The microstructures were investigated by optical microscopy and scanning electron microscopy (SEM). More homogeneous dispersion of Al₂O₃ in the Al matrix, and hence improved mechanical properties of the composites, was achieved with increased milling time. The best mechanical properties were produced after 3-h milling, because of the homogeneous distribution of the reinforcing materials.