Superplastic Characteristics of β-Si3N4 Whisker Reinforced 6061Al Alloy Composite Fabricated by Squeeze Casting

β-Si3N4 whisker reinforced 6061 aluminum alloy composite fabricated by squeeze casting was extruded with the extrusion ratios of R=44 and R=100 at 773 and 803 K. The tensile strength and superplastic characteristics of the composite were investigated. The composite indicates the tensile strength of 400 MPa at room temperature and about 250 MPa at 573 K. The composite extruded with R=100 exhibits the m value of 0.31 in the strain rate range from 0.01 to 1.07 s−1 and the total elongation of 173% at the strain rate of 0.02 s−1. The whisker reacted with 6061 aluminum alloy so as to synthesize AlN and make Si soluble to the matrix at interfaces. Therefore, an interfacial sliding in semi-solid condition might occur during superplastic deformation. The grain sizes of the composite heated up at 818 K and deformed superplastically was under 3 μm which is almost the same size of the composite fabricated by PM method before extrusion. The difference of superplastic characteristics in the composite between squeeze casting and PM method routes might be associated to subgrain behavior.