The optimization of ECAP conditions to achieve high strain-rate superplasticity in a Zr- and Sc-modified AA 7075 aluminum alloy

An AA 7075 aluminum alloy with Zr and Sc additions was subjected to 6-8 passes of equal-channel angular pressing at 120, 170, and 220 degrees C in order to study the effect of the pressing conditions on the microstructural characteristics and the consequences for high-temperature mechanical properties. Using the method of electron backscatter diffraction, a decrease in pressing temperature was found to lead to a more pronounced refinement of the microstructure and a higher fraction of high-angle grain boundaries, but at the same time compromised the ability of the Al(3) (Zr, Sc) phase to stabilize the ultra-fine-grained microstructure at elevated temperatures. Optimum superplastic properties were therefore achieved after pressing at the intermediate temperature of 170 degrees C. The material exhibited high strain-rate superplasticity with a ductility of 650% at an initial strain rate of 1 x 10(-1) s(-1).