The influence of compocasting variables (SiC size and %vol, additions of grain refiner and extra Mg) in the quality of A356 + SiCp MMCs is investigated. In all conditions microstructures show Al-alpha with globular morphology with eutectic and SiC in interglobular regions. Results show tendency of agglomeration of thinner particles, jeopardising their incorporation and dispersion in the matrix; high quantities of SiC are not incorporated into rheocast slurries with refined globules, grain refinement decreases incorporation of bigger particles. Extra Mg does not influence incorporation. Best results are obtained for 15%vol of 30mum SiC added to grain refined matrix. Mechanical properties are poor when agglomeration of particles is present.