Superplasticity in a 7055 aluminum alloy processed by ECAE and subsequent isothermal rolling

The superplastic properties and microstructural evolution of a 7055 aluminum alloy was examined in tension at temperatures ranging from 300 to 450 degrees C and strain rates ranging from 2.7 x 10(-5) to 5.6 x 10(-2) s(-1). A refined microstructure with an average grain size of similar to 1.4 mu m and a portion of high-angle grain boundaries (HAGBs) of similar to 67% was produced in sheets by equal channel angular extrusion (ECAE) followed by isothermal rolling (IR) at 250 degrees C. The alloy exhibited a maximum elongation-to-failure of similar to 820% at a temperature of 450 degrees C and an initial strain rate of 5.6 x 10(-3) s(-1). Superplastic elongation of similar to 670% was recorded at strain rates higher than 10(-2)s(-1), where the strain rate sensitivity coefficient was around 0.44. The relationship between superplastic ductilities and microstructure stability was analyzed. It was shown that increasing the portion of HAGBs by IR results in enhancement of superplastic properties. (c) 2005 Elsevier B.V. All rights reserved.