The wettability of all ceramic particles is poor with molten aluminum except for SiC and to some extent for Al2O3. It is related to the surface energy of the particles in relation to the aluminum melt. Various methods are adopted by researchers to enhance the wettability of ceramic particles with molten aluminum. All the methods would essentially improve the surface energy to be wetted by liquid aluminum. The size of the particles also would have an indirect effect on the wettability and reduce the volume fraction of the reinforcement particles in an aluminum composite achievable by stir casting techniques. Please refer the following articles
The enhancement of wettability of SiC particles in cast aluminium matrix composites, Journal of Materials Processing Technology 119 (2001) 329-335.
The reactive wetting and incorporation of B4C particles into molten aluminium, Scripta mater. 44 (2001) 1077–1082