EFFECT OF HOT EXTRUSION ON THE MECHANICAL-PROPERTIES OF SIC WHISKER AZ91 MAGNESIUM ALLOY COMPOSITES

Cast and extruded composites of SiC whisker reinforced AZ91 magnesium alloy were fabricated by high pressure infiltration of the alloy melt into preformed whiskers and subsequent hot extrusion. Structures, age hardening behavior and mechanical properties were examined on the obtained composites, and the effect of hot extrusion was discussed. Unidirectional alignment of whiskers was attained by hot extrusion of the cast composites with a sacrifice of appreciable decrease of aspect ratio of whiskers. Such structural changes caused an increase of elastic modulus and a slight decrease of the strengthening effect of whiskers for tensile strength in the extruded composites. At elevated temperatures, lower tensile strength and higher ductility were observed for the extruded composites than for the cast ones. The extruded composites in T6 temper showed much higher specific elastic modulus than titanium alloys or maraging steels, and higher specific tensile strength than high strength aluminum alloys.