Evolution of texture and grain misorientation in an Al-Mg alloy exhibiting low-temperature superplasticity

Abstract

Low-temperature superplasticity (LTSP) at 250 °C and 1 × 10−3 s−1 was observed in a 5083 Al-Mg base alloy after thermomechanical treatments (TMTs). With a higher TMT rolling strain, the fraction of high-angle grain boundaries increased, which was favorable for the further operation of grain-boundary sliding (GBS) and LTSP. The near-brass {110}〈112〉, S {123}〈634〉, and Cu {112}〈111〉 texture components in the as-thermomechanically treated specimens gradually evolved into a random orientation distribution during LTSP straining from 30 to 100 pct. Static annealing at 250 °C itself could not alter the existing texture. The grain-misorientation distribution curves also showed that, after 100 pct LTSP elongation, the misorientation angles approached the random distribution. In the latter case, the low-, medium-, and high-angle boundaries each would partition around 10, 20, and 70 pct, respectively. When the LTSP elongation was greater than 150 pct, the macrodeformation anisotropy (R) ratio would reach a plateau value of ∼0.8. During the initial stage, a group of over 60 grains proceeded cooperative grain-boundary sliding (CGBS); most individual grain boundaries started to slide at the later stage. It seems that it is the high-angle boundaries, not the special coincidence-site lattice (CSL) boundaries, which could govern the LTSP performance.