The activation energy for superplastic flow in Al-6Cu-0.4Zr

Abstract

A study of the activation energies for superplastic flow in an essentially single phase Al-6Cu-0.4Zr alloy has been made in the temperature range 430 to 490° C. Straight line Arrhenius plots for bothQ _σ and$Q_{\dot \in }$ were obtained in Regions I, II and III. In all cases the ratio$Q_{\dot \in } /Q_\sigma$ corresponded well to the average strain rate sensitivity as determined by both change rate testing and from the slope of the Inσ versus In$\dot \in$ curves. Values ofQ _σ of 35.2, 19.0 and 20.1 kcal mol⁻¹ were obtained in Regions I, II and III respectively. These values were expected to be close to the true activation energies, and corresponded to the measured lattice and predicted grain boundary diffusion activation energies. These energies, together with microstructural observations made on deformed material, were used to identify possible deformation mechanisms.