Superplasticity behaviors of Al-Zn-Mg-Zr cold-rolled alloy sheet with minor Sc addition

A refined microstructure of Al-Zn-Mg-Sc-Zr alloy sheet was produced by simple hot and cold rolling to an average grain size of 3 mu m. Experiments were completed in electro-fluid servo-fatigue tester and results were investigated by means of optical microscope (OM), scanning electron microscopy (SEM) and transmission electron microscope (TEM). Superplastic deformation was conducted and superplastic ductility of 200% was achieved at a testing temperature range from 425 QC to 500 degrees C and relative high strain rate range of 1 x 10(-3) s(-1)similar to 1 x 10(-1) s(-1). The maximum elongation of 539% was obtained at 500 degrees C and 1 x 10(-2) s(-1). In addition, the scanning electron microscopy (SEM) and transmission electron microscope (TEM) analyses showed that the presence of Al-3 (Sc, Zr) particles in pinning grain boundaries and dislocations had a great influence on the superplastic deformation. The analyses of superplastic test data calculated out the coherent strain rates sensitivity parameter of 0.43 and the average activation energy of 143.762 kJ/mol. The data interpreted that the dominant deformation mechanism was grain boundary sliding controlled by lattice self-diffusion. (C) 2016 Elsevier B.V. All rights reserved.