Tensile specimens of an Al-24 wt % Cu alloy of grain sizes in the range 7.6-20.6 mu m were deformed at 400-540 degrees C using constant initial strain rates ranging from 5 x 10(-6) to 2 x 10(-2) s(-1). Initially the stress-strain (sigma-epsilon) curves show work hardening which is followed by strain softening at higher strain rates and lower temperatures. At lower strain rates and higher temperatures, on the other hand, sigma continues to increase with strain or tends to be independent of strain. Grain growth and cavitation occur to varying extents depending on strain rate and test temperature. While the grain growth can account for the work hardening at higher temperatures as well as at lower strain rates, it fails to do so at higher strain rates. The strain softening is associated with cavitation. The presence of non-steady-state flow influences the parameters of the constitutive relation to varying extents.