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

Abstract 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 SiC P (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 SiC P throughout the matrix was achieved at a volume fraction as high as 7 vol%. Average α–Al dendritic sizes were significantly refined from 270 µm for the matrix to 90 µm in the solidified microstructure of nanocomposites. Thermal analysis during solidification indicates that the presence of nanosized SiC P increased the nucleation temperature of α–Al, whilst recalescence during solidification process disappeared. Additionally, the yield and ultimate tensile strength of the nanosized SiC P /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 SiC P at ambient temperature could be attributed to thermal mismatch strengthening, Orowan strengthening and grain refinement strengthening, while the pinning effect of nanosized SiC P could predominantly account for the strengthening effect at 453 K. Highlights • Nanosized SiC P refined the microstructure via heterogeneous nucleation and inhibited growth. • SiC P enhanced strengths at 298 K mainly due to thermal mismatch and Orowan strengthening. • Pinning effects of SiC P on grain boundaries and dislocation climbing enhanced strengths at 453 K. [ABSTRACT FROM AUTHOR]