The present invention relates to modifying the properties of a metal matrix composite body by a post formation process modification treatment. The post formation process treatment may be applicable to a variety of metal matrix composite bodies produced by various techniques, and is particularly applicable to modifying the properties of a metal matrix composite body produced by a spontaneous infiltration technique. Particularly, at least a portion of the matrix metal of the metal matrix composite body and/or the filler material of the metal matrix composite body is modified or altered after the formation process. Preferably, the preform contains a second non-metal material, an infiltration enhancer of infiltration enhancer precursor, and an infiltration atmosphere.