The physical phenomena of solidification and the mechanical properties of aluminum matrix composites are reviewed.Nucleation and growth of the matrix, solute distribution and fluid flow in the cast aluminum matrix composites are changed by the addition of reinforcers, especially in the case of nonequilibrium solidification under differential pressure and under variation of the cooling conditions. Such changes greatly influence the dendrite structure of matrix, precipitation, solute segregation, interface reactivity, solidification defects etc., and properties of the composites.