Grain structure, texture evolution and deformation mechanism during low temperature superplasticity in 5083 Al-Mg alloy

Low temperature superplasticity (LTSP) was observed in the 5083 Al-Mg base alloy after thermomechanical treatments (TMT). The maximum LTSP elongation was 400%, occurring at 250 degrees C and 1 x 10(-3) s(-1). The subgrain str uctures formed during TMT transformed to better defined subgrains to simila r to 0.5 mu m upon heating to 250 degrees C. Further static annealing or su perplastic straining at 250 degrees C would produce well defined fine grain s to 1.5-2.5 mu m, dependent on annealing time or strain level. Superplasti c loading would accelerate grain evolution rate. The near brass {110}[112] and S {123}[634] texture components in the as-TMT specimens evolved into a random orientation distribution after LTSP loading to 100% at 250 degrees C . Static annealing at 2500C itself could not alter the existing texture. Un der the optimum LTSP condition, the Q-value was similar to 0.5, compared wi th 0.2 for the as-received coarse-grained 5083 alloy. The activation energy e-value was around 50-90 kJ/mol for LTSP over 200-300 degrees C and around 145 kJ/mol for HTSP over 400-550 degrees C. It is postulated that the rate controlling deformation mechanism in the TMT processed specimens was grain boundary sliding during the optimum LTSP condition and solute drag creep d uring HTSP deformation.