M40J carbon fiber reinforced aluminum-2.4, 4.7 and 10mass% magnesium alloy composite wires were continuously fabricated using ultrasonic infiltration method. The tensile strength of the composites varied from 800 to 1200 MPa caused by change in cross sectional area, volume fraction of fibers and so on. Moreover, their tensile strength decreased with the increase in Mg content in aluminum. In the case of the Al-10mass%Mg matrix composites, Al3Mg2 intermetallic compound was found on the surface of fibers and continuously formed between fibers in the matrix like bridging. The decrease in the strength would be caused by premature fracture and bridging of the intermetallic compound between fibers. As the result, the tensile strength of the CF/Al composites was controlled by cross sectional area and amount and shape of Al3Mg2 intermetallic compound in aluminum matrix.
