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

Low-temperature superplasticity (LTSP) at 250 degrees C and 1 x 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 gra in-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 pet. Static annealing at 250 degrees C itself could not alter the existing texture. The grain-misorientation distributio n curves also showed that, after 100 pet LTSP elongation, the misorientatio n angles approached the random distribution. In the latter case, the low-, medium-, and high-angle boundaries each would partition around 10, 20, and 70 pet, respectively. When the LTSP elongation was greater than 150 pet, th e macrodeformation anisotropy (R) ratio would reach a plateau value of simi lar to 0.8. During the initial stage, a group of over 60 grains proceeded c ooperative grain-boundary sliding (CGBS); most individual grain boundaries started to slide at the later stage. It seems that it is the high-angle bou ndaries, not the special coincidence-site lattice (CSL) boundaries, which c ould govern the LTSP performance.