Superplastic deformation mechanisms of a fine-grained Al-Cu-Li alloy

The superplastic flow behavior and microstructural evolution of a fine-grained Al-Cu-Li alloy deformed at a temperature of 490 degrees C and an initial strain rate of 2 x 10(-4) s(-1) were studied by electron backscatter diffraction, scanning electron microscope and focused ion beam techniques. Based on the obtained data, the contributions of grain boundary sliding and intragranular dislocation slip to superplastic deformation of the Al-Cu-Li are carefully calculated. The results show that the whole superplastic deformation process can be divided into three stages. Strain from 0 to 0.1 can be identified as the strain hardening stage, in which dislocation movement is the main deformation mechanism and grain boundary sliding is the accommodation mechanism, multiplication of dislocation leads to strain hardening. Strain from 0.1 to 1.2 can be identified as the nearly steady flow stage, in which the grains are nearly equiaxed, the average grain size increases slowly and the proportion of high angle grain boundaries increases. Moreover, with the increase of the strain, the contribution of grain boundary sliding on deformation decreases gradually. The strain softening caused by dynamic recrystallization was observed at the end of this stage. The third stage is another strain hardening stage, in which rapidly dynamic grain growth and dislocation slip result in the strain hardening. The current research results emphasize that the diffusion creep is mainly responsible for the superplastic deformation, and the grain boundary sliding and intragranular dislocation slip play an accommodating role.