PURPOSE: To improve the strength of an Al alloy composite using Si3N4 coated aluminum borate whiskers as a reinforcing material.

CONSTITUTION: The objective Al alloy matrix for a composite uses aluminum borate whiskers having an Si3N4 coated layer on the surface as a reinforcing material. This Al alloy matrix contains, by weight, 3 to 6% Cu and 2.2 to 4% Mg or 3 to 6% Cu, 2.2 to 4% Mg, 0.4 to 0.8% Mn and 0.2 to 0.6% Fe.