Superplasticity in a 7055 aluminum alloy subjected to intense plastic deformation

Superplasticity in a 7055 aluminum alloy subjected to intense plastic straining through equal channel angular extrusion (ECAE) was studied in tension over a range of strain rates from 1(.)4 x 10(-5) to 5(.)6 x 10(-2) s(-1) in the temperature interval 300 - 450degreesC. The alloy had a grain size of similar to1 mum. A maximum elongation to failure of similar to 750% occurred at a temperature of 425degreesC and an initial strain rate of 5(.)6 x 10(-4) s(-1), with a strain rate sensitivity coefficient m of about 0(.)46. The highest m value was similar to0(.)5 at a strain rate of 1(.)4 x 10(-3) s(-1) and Tgreater than or equal to425degreesC. Moderate superplastic properties with a total elongation of about 435% and m of similar to0(.)4 were recorded in the temperature interval 350-400degreesC; no cavitation was found. It was shown that the main feature of superplastic behaviour of the ECAE processed 7055 aluminum alloy is a low yield stress and strong strain hardening during the initial stages of superplastic deformation. Comparing the present results with the superplastic behaviour of the 7055 Al subjected to thermomechanical processing (TMP), the highest tensile elongation in the ECAE processed material occurred at lower temperatures because ECAE produces a finer grained structure.