An aluminum metal matrix composite comprises an aluminum metal matrix embedding a second filler, such as a ceramic second filler, and is formed by contacting, for example, a molten aluminum metal with a permeable mass of second filler within a ceramic impervious mold formed by growing a polycrystalline oxidation reaction product into a first filler. By hermetically sealing the second filler within the mold with a body of molten aluminum metal, the latter spontaneously infiltrates the mass of second filler at moderate temperatures, e.g. about 900.degree. C., without need of any other infiltration expedients. The molten mass containing the infiltrated ceramic filler is solidified to provide the metal matrix composite which may be recovered from the mold. Optionally, the solidification is carried out under bonding conditions including maintaining the solidifying material in direct contact with the ceramic mold, to provide the metal matrix composite joined to the mold, or a part thereof, as a structural component.