Short fiber preform, method of making it, and composite material manufactured from it

A method for making a composite material wherein a matrix material selected from the group consisting of magnesium alloy and aluminum alloy is reinforced by fibers embedded therein, and wherein said method comprises:

• a) preparing a mass of a mixture of fibers selected from the group consisting of alumina, carbon, potassium titanate, alumina-silica and silicon carbide fibers and an inorganic binder of silica or alumina, said binder being in such a partially dried condition that said mass is uniformly deformable under compression;
• b) compressing a portion of said mass with said binder being in said partially dried condition so as to increase the density of said fibers in said portion from that in the remainder of said mass, and wherein for said compression, a first portion of the moist mass is substantially compressed, a second portion of the moist mass is compressed to a relatively low extent, and a third portion, joining between said first portion and said second portion, is compressed by an amount which changes substantially continuously from the portion adjoining to said first portion to the portion adjoining to said second portion;
• c) drying said mass to harden said binder;
• d) infiltrating under pressure a molten alloy selected for said matrix into interstices of said mass to fill said interstices while substantially maintaining a fiber work structure of said mass under the binding force of said binder;
• and
• e) solidifying said molten alloy with said fiber work structure of said mass being embedded in the matrix of said alloy.