Superplasticity in an 7475 Aluminum Alloy Subjected to Equal Channel Angular Extrusion

摘要

Superplastic behavior of a high-strength 7475 aluminum alloy subjected to intense plastic straining through equal-channel angular extrusion (ECAE) was studied in tension at strain rates ranging from 1.4×{sup}(-3) to 5.6×10{sup}(-2) s{sup}(-1) in the temperature interval 400-450°C. Microstracture of the 7475 aluminum alloy after ECAE was non-uniform. Volume fraction of fine grains with average size of about 1.2μAm was ～60%. These grains alternate with elongated grains having longitudinal size of ～5 urn. The highest elongation-to-failure of ～470% was attained at a temperature of 425°C and an initial strain rate of 1.4×10{sup}(-2) s{sup}(-1) with the corresponding strain rate sensitivity coefficient, m, of 0.37. It was shown that the main feature of superplastic behavior of the ECAE processed 7475 aluminum alloy is an extensive strain-hardening at initial stages of superplastic deformation attributed to instability of microstructure.