In situ synthesis of nanocrystalline Al6063 matrix nanocomposite powder via reactive mechanical alloying

In this work, nanocrystalline Al6063 composite powder reinforced with nanometric oxide ceramic particles was synthesized via an in situ solid-gas reaction during high-energy mechanical alloying under a mixture of argon-oxygen atmosphere. The effect of oxygen volume fraction on the morphological evolution and microstructural changes during mechanical alloying was studied by various analytical techniques including optical and electron microscopy, X-ray diffraction, laser particle size analysis, apparent density measurement, and microhardness test. The reactive mechanical alloying resulted in the formation of amorphous Al- and Al-Mg-Si-Fe oxides with a size range of 40-100 nm and volume fraction up to ∼2.6 vol.% dependent on the oxygen partial pressure. Electron microscopy studies revealed formation of equiaxed grains with a wide size distribution ranging from 60 to 260 nm. Meanwhile, finer particles with narrower size distribution were achieved at a shorter milling time when the in situ solid-gas reaction was employed. Results of compression test and hardness measurement on the hot extruded powders at 450 °C with an extrusion ratio of 14:1 revealed a significant improvement in the mechanical properties caused by the nanometric ceramic particles as well as the ultrafine grain structure of the matrix.