Superplasticity-dislocation creep interactions in a coarse grained Al-Cu-Zr alloy

Abstract

Specimens of a relatively coarse-grained Al-5.8Cu-0.39Zr (wt %) alloy were deformed at 730 K in tension by various amounts and at several strain rates. By comparing the grip and gauge (deformed) portions of each tested sample, taking into account the variations in the initial texture and using an orientation distribution function evaluation, the texture changes due to superplastic flow were identified. Crystallographic slip is shown to be significant only beyond the strain-rate range for maximum elongation. At lower strain rates, grain/interphase boundary sliding appears to control the deformation. The accompanying grain rotation causes a general weakening of the initial texture. It is also shown that evaluating an average value of the strain-rate sensitivity index, m, from a double logarithmic plot of the flow stress and true strain rate is inadequate for delineating the ranges of operation of different mechanisms. Instead, the evaluation of m by the changing strain rate method is advocated.