Fabrication, microstructure refinement and strengthening mechanisms of nanosized SiCP/Al composites assisted ultrasonic vibration

The performances of particulate-reinforced aluminum matrix composites are strongly dependent on alloying elements, precipitates and added particulates. To reveal the sole influence mechanisms of high volume fraction of nanosized particulates on the solidification behavior, microstructure and mechanical properties of aluminum alloys, nanosized SiCP (60 nm) was incorporated into commercial pure Al at different volume fractions (i.e., 0, 1, 3, 5, 7 and 9 vol%) by stir-casting assisted ultrasonic vibration. The results reveal that a fairly uniform dispersion of nanosized SiCP throughout the matrix was achieved at a volume fraction as high as 7 vol%. Average alpha-Al dendritic sizes were significantly refined from 270 mu m for the matrix to 90 mu m in the solidified microstructure of nanocomposites. Thermal analysis during solidification indicates that the presence of nanosized SiCP increased the nucleation temperature of alpha-Al, whilst recalescence during solidification process disappeared. Additionally, the yield and ultimate tensile strength of the nanosized SiCP/Al composites at both ambient temperature and 453 K were remarkably improved, whilst remaining suitable fracture strain. Theoretical analysis suggests that the significant strength increments induced by nanosized SiCP at ambient temperature could be attributed to thermal mismatch strengthening, Orowan strengthening and grain refinement strengthening, while the pinning effect of nanosized SiCP could predominantly account for the strengthening effect at 453 K.