Process for preparation of composite materials containing nonmetallic particles in a metallic matrix

A method for preparing a composite of aluminum alloy reinforced with silicon carbide particles, comprising:

• roasting the silicon carbide particles at a temperature of at least about 800.degree. C. in a gaseous source of oxygen, for a time sufficient to form a zone at the surface of the particles wherein the carbon content is less than about 25 percent of its initial level, the depth of the zone being at least about 50 Angstroms below the surface of the particles;
• forming a mixture of the molten aluminum alloy and the roasted particles;
• maintaining the mixture in a temperature range of from about the liquidus temperature of the metallic material to a temperature whereat the particles do not substantially degrade during the time required for the subsequent processing steps;
• mixing together the particles and the molten metal for a time sufficient to wet the molten metal to the particles and to distribute the particles throughout the molten metal, using a rotating dispersing impeller immersed in the molten mixture to shear the particles and the molten metal past each other while minimizing the introduction of any gas into the mixture and while minimizing the retention of any gas already present in the mixture, said step of mixing to occur with a vacuum applied to the mixture;
• and
• casting the resulting mixture.