Effect of the particle size and volume fraction on superplasticity of SiC_p/6061 aluminum alloy composite

Effects of particle size and volume fraction of SiC particle on superplastic characteristics of SiC_p/6061 aluminum alloy composites made by a vortex method before squeeze casting, extrusion and hot rolling were investigated in order to make clear the superplastic deformation mechanism. Flow stress of the SiC_p (0.6 μm)/6061 aluminum alloy composite decreased with increasing the volume fraction in the case of the volume fraction of 0.13 and 0.20, and the m value became 0.30∼0.46 in the initial strain rate region of more than 2.4 × 10^-1 s^-1, and the maximum total elongation more than 200% was obtained at 853 K. And also, SiC_p (1.2 μm) /6061 aluminum alloy composite exhibited m value of 0.32 at an initial strain rate of 7 × 10^-2 s^-1 and maximum total elongation of about 170%. However, 5 and 10 μmSiC_p/6061 aluminum alloy composites did not produce superplasticity. It is thought that in SiC_p/6061 aluminum alloy composite made by a vortex method, V_f=0.20 is optimum volume fraction for maximum total elongation. The threshold stress of the composites decreased with increasing SiC volume fraction. The stress exponent (n) indicated 3 for the creep deformation in the case of SiC_p (5 and 10 μm) /6061 aluminum alloy composites, n showed 2 for the superplastic deformation in the case of SiC_p (0.6 and 1.2 μm) /6061 aluminum alloy composites. On and near the fracture surface of the composite after superplastic deformation, filaments and striation bands were formed at sliding grain boundaries and interfacial sliding were observed and it is thought that high strain rate superplasticity of the composite could occur by grain boundary sliding and liquid phase accommodation mechanisms.