Superplastic deformation mechanisms of particulate reinforced aluminum matrix composites

Superplastic tensile tests of a SiC_p reinforced 8090 aluminum alloy composite were carried out at strain rates ranging from 7.25 × 10^-4 to 3.46 × 10^-1 s^-1 and at temperatures from 773 to 873 K. A maximum elongation of 300% was obtained at a strain rate of 1.83 × 10^-1s^-1 when tested at a temperature of 848 K which was slightly above the solidus temperature of the composite. Several important superplastic factors such as strain rate sensitivity, threshold stress and activation energy were calculated. The superplastic behavior of some particulate reinforced aluminum alloy based composites and several aluminum alloys was compared in view of the strain rate, the optimum testing temperature and the relationship between the flow stress and the strain rate. Considering the accommodation process for dislocation movements, the constitutive equations for superplastic deformation at temperatures above and below the solidus temperature of the composite were developed. Experimental results of the stress-strain relationship obtained at temperatures near to the solidus temperature of the composite compare well with the theoretical constitutive predictions.