Abstract
A 7475-aluminum alloy was subjected to a thermomechanical heat treatment that resulted in a final recrystallized grain size on the order of 10 mu m. Tensile specimens of dimensions 10 4 2.3 mm were machined such that the tensile axis was parallel to the rolling direction. Tensile tests were carried out at high temperatures in the range of 773 to 803 K at different cross-head speeds corresponding to initial strain rates in the range of 10 super(-4) to 10 super(-2) s super(-1). Elongations of several hundred percent were observed at strain rates of <10 super(-3) s super(-1). The correlation between flow stress and strain rate suggests that the strain rate sensitivity m is close to 0.5 at the lower strain rates. The value of m decreases to approximately 0.2 at high strain rates. The decrease in m suggests a transition in the rate-controlling process from superplastic deformation (m approximately 0.5) to dislocation creep (m approximately 0.2) with increasing strain rate. The calculated activation energies in the two deformation regions are consistent with the suggested rate-controlling processes.