PURPOSE: To relieve thermal stress and to increase the strength of a metal matrix composite material as a whole by performing cooling treatment down to a specific temp. at the time of heat treatment of a metal matrix composite material.

CONSTITUTION: A process, where cooling is done down to low temp. at least once, is added to the heat treatment process for a metal matrix composite material where metal (alloy) is used as matrix and ceramics and metal are used as reinforcement. It is preferable to regulate the cooling temp. to ≤0°C. Because thermal stress is relieved by the cooling, a crystallographical dislocation is generated in the matrix of the metal matrix composite material and the matrix is strengthened, and consequently, the whole metal matrix composite material is also strengthened and superior strength characteristics can be obtained. In this cooling process, the rate of change in temp. in a cooling stage down to a specific temp. is made dissimilar to that in a subsequent temp. rise stage, by which dislocation density increased by cooling is moved in the direction of dislocation source in the temp. rise stage to prevent the dissipation of the dislocation density in the interface between the reinforcement and the matrix.