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

摘要

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℃and 1×10{sup}(-3)s{sup}(-1) The subgrain structures formed duringTMT transformed to better defined subgrains to ~0.5μm upon heating to 250℃. Further static annealing or superplastic straining at 250℃ would produce well defined fine grains to 1.5-2.5μm, dependent on annealing time or strain level. Superplasticloading 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℃. Static annealing at 250℃ 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℃ and around 145 kJ/molfor HTSP over 400-550℃. 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.