The optimization of ECAP conditions to achieve high strain-rate superplasticity in a Zr- and Sc-modified AA 7075 aluminum alloy
Abstract
An AA 7075 aluminum alloy with Zr and Sc additions was subjected to 6-8 ECAP passes at 120, 170, and 220 °C in order to examine the effect of the pressing conditions on the microstructural characteristics and the consequences for high-temperature mechanical properties. Using the method of EBSD, 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 Al3 (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 °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.