Characterization and mechanical properties of α-Al2O3 particle reinforced aluminium matrix composites, synthesized via uniball magneto-milling and uniaxial hot pressing

Al-based composite powders containing 2, 4, 7 and 10 volume fraction of α-Al2O3 were prepared using the uniball controlled magneto-milling method and were then uniaxially hot pressed at (600 ± 10)°C under 70 MPa for 15 min. The resulting composites were greater than 99% theoretical density with enhanced mechanical properties. Detailed characterization was performed using: X-ray diffraction, scanning electron microscopy equipped with energy dispersive spectroscopy, electrical conductivity, compression, ultra-micro indentation testing and pin on drum wear testing at ambient temperature. Microstructure-mechanical property correlations were obtained as functions of α-Al2O3 volume fraction. It was found that controlled milling resulted in an uniform distribution of the hard α-Al2O3 particles within the Al, an acceleration of Al hardening and fracturing, and strain accumulation by the Al matrix. Hardness, strength, wear resistance and electrical resistivity of the monolithic products increased with increasing the volume fraction of α-Al2O3 up to 10 vol.%. These were: HV = (1.84 ± 0.26) GPa, maximum compressive strength = (845 ± 33) MPa, compressive yield strength = (515 ± 11) MPa. Outcomes were interpreted in light of the structural defects induced by milling, the presence of α-Al2O3, and dispersion of iron milling contaminants, with additional effects caused by oxygen introduced during the milling and/or the heat treatment.