Properties of SiCp/Al and SiCw/SiCp/Al composites prepared by mechanical alloying and the powder metallurgy process

In order to prepare SiCw/SiCp/Al duplex composites, SiCp was dispersed in Al by mechanical alloying and subsequently reinforced with SiCw by powder metallurgy. Mechanical alloying was carried out for 10 h by using an Attritor ball mill with addition of methanol. Mechanically alloyed powder which was mixed with SiCw was used for hot press and hot extrusion. The microstructures and mechanical properties were examined on the extruded composites. Uniform distribution of SiCp and SiCw was obtained in both composites with 100% relative density. SiCp/Al composites show a drastic increase of tensile strength by dispersion strengthening, while their elastic modulus remained nearly the same. Tensile strength and elastic modulus of SiCw/SiCp/Al composites increased with increasing SiCw volume fraction. Dispersion strengthening attained by mechanical alloying was higher than strengthening by SiC whiskers in composites. SiC whiskers of smaller diameter (0.45 mu m) show higher strengthening effect than those of larger diameter (1.2 mu m) The highest tensile properties were obtained in the SiCw/SiCp/Al duplex composites; tensile strength 565 MPa and elastic modulus 105 GPa at room temperature, and tensile strength 233 MPa at 573 K.