Nanoparticulate dispersion, microstructure refinement and strengthening mechanisms in Ni-coated SiCp/Al-Cu nanocomposites

Ni-coated SiCp/Al–Cu nanocomposites with different addition levels (0, 1, 2 and 3 wt% Ni-coated SiCp nanoparticulates) were successfully fabricated by semisolid stir casting combined with hot extrusion. The microstructures of the as-cast and hot-extruded nanocomposites showed that the grain size could be substantially refined. The dispersion mechanism of the SiCp nanoparticulates was discussed. Because the Al3Ni that was formed on the SiCp surface improved the wettability, more Ni-coated SiCp nanoparticulates were captured as the solid/liquid interface advanced, causing the Ni-coated SiCp to enter the α-Al interior and reduce agglomeration in the grain boundaries. The strengthening mechanism of the SiCp nanoparticulates at room temperature and high temperatures was studied. At 298 K, the strengthening was attributed to the hindrance of dislocation movement by the uniformly distributed SiCp nanoparticulates, grain size refinement and thermal mismatch strengthening. At 453 K and 493 K, the strengthening effect was ascribed to the impeded dislocation climb by the SiCp nanoparticulates distributed in the grain interior and the pinning effect of nanoparticulates on the grain boundaries.