Grain Structure, Texture Evolution and Deformation Mechanism during Low Temperature Superplasticity in 5083 Al–Mg Alloy

Abstract

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°C and 1×10−3 s−1. The subgrain structures formed during TMT transformed to better defined subgrains to ∼0.5 μm upon heating to 250°C. Further static annealing or superplastic straining at 250°C would produce well defined fine grains to 1.5–2.5 μm, dependent on annealing time or strain level. Superplastic 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°C. Static annealing at 250°C itself could not alter the existing texture. Under the optimum LTSP condition, the m-value was ∼0.5, compared with 0.2 for the as-received coarse-grained 5083 alloy. The activation energy Q-value was around 50–90 kJ/mol for LTSP over 200–300°C and around 145 kJ/mol for HTSP over 400–550°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 during HTSP deformation.