Synthesis of nanostructured Al–Mg–SiO₂ metal matrix composites using high-energy ball milling and spark plasma sintering

Abstract

Mechanical alloying by high-energy ball milling is successfully used to produce a metal matrix composite of Al–Mg reinforced with amorphous silica particulate. Four different compositions are chosen with varying Mg content (0.5, 1, 2.5 and 5 by wt.%) by keeping SiO₂ content constant at 5 wt.% to make nanocomposites by high energy ball milling and microcomposites by mechanical mixing. No new phases are found in 20 h mechanically alloyed Al–Mg– SiO₂ metal matrix composite. XRD study showed Mg is completely dissolved into the Al matrix. XRD observation also showed decrease in crystallite size and increase in lattice strain with progress of mechanical alloying. SEM micrographs indicate decrease in particle size via fracture and cold welding phenomena. The powders are made in the form of cylindrical pellets of 20 mm diameter by Spark Plasma Sintering. X-ray diffraction analysis of the pellets obtained after sintering indicates the evolution of MgAl₂O₄ spinel structure along with Al₂O₃. Vickers hardness values observed for nanocomposites are more than twice as high as that of microcomposites.