High strain rate superplasticity in aluminum matrix composites

Recently, several studies have demonstrated that a variety of metallic materials, including aluminium-based composites, can exhibit superplasticity at relatively high strain rates (≥10-2s-1). High strain rate superplasticity (HSRS) is very attractive for commercial applications, mainly for materials difficult to shape or machine with conventional techniques, such as metal matrix composites. In this work, the possibility of achieving HSRS in a recently developed composite with an AA6013 matrix reinforced with about 20 vol % of SiC particles (AA6013/20/SiCp) was studied. Uniaxial tensile tests were carried out at high strain rates (1 x 10-1s-1 and 1 x 10-2s-1) and in a temperature range between 520 and 590°C. A maximum elongation-to-failure of 370 per cent was obtained at 560°C with a strain rate of 1 x 10-1s-1. This temperature is very close to the temperature at which melting of the composite starts. Scanning electron microscopy (SEM) analyses of fracture surfaces in the optimum superplastic condition showed the presence of filaments, the formation of which generally related to the presence of a liquid phase at the grain boundaries and/or at the interfaces.