抄録
The Si3N4 particulate reinforced 6061Al(Al-Mg-Si) matrix composite, which included 20% or 30% volume fraction of reinforcement, denoted as the 20%Vf and the 30%Vf respectively, has been produced by powder metallurgical processing followed by hot extrusion at 773K with a reduction ratio of 100. The composites exhibited a typical superplastic behavior at a temperature of 848K for the 20%Vf and 823K for the 30%Vf, and a maximum elongation of 380% was obtained for the 20%Vf at a constant stress of 5MPa and 734% was obtained for the 30%Vf at a stress of 8MPa respectively. It has been clarified that these composites exhibited cavitation after a superplastic deformation. Cavity volume fractions exponentially increased with increasing strain in both composites. The cavity volume fraction of the 20%Vf specimen was less than that of the 30%Vf specimen at a strain up to 1.2. The maximum cavity volume fraction throughout the experiments was 2% at a strain of 1.5 for the 30%Vf specimen. SEM obsevation showed that cavities had always formed at interface between matrix and reinforcements, and the size of most cavities was less than 1μm. However, a few large cavities of more than 1μm in a mean diameter also appeared in both specimens in an early stage of straining. The larger cavities were grown rapidly and elongated parallel to the tensile axis with increasing strain which may cause the fracture.
