Metal matrix composites generally have bad wetting between particle and matrix. This problem may be avoided if the improving phase is introduced in the matrix by means of an in-situ reaction. The heating of the matrix initiates reactions between different elements, forming new phases. The main advantage of the in-situ introduction of an improving phase will be the expected homogeneous distribution of particles in the melt and good interfacial contact. Forces acting on the particles in the melt and during solidification cause an heterogeneous distribution of the particles.