Deformation mechanisms in superplastic AA5083 materials

The plastic deformation of seven 5083 commercial aluminum materials, produced from five different alloy heats, are evaluated under conditions of interest for superplastic and quick-plastic forming. Two mechanisms are shown to govern plastic deformation in AA5083 over the strain rates, strains, and temperatures of interest for these forming technologies: grain-boundary-sliding (GBS) creep and solutedrag (SD) creep. Quantitative analysis of stress transients following rate changes clearly differentiates between GBS and SD creep and offers conclusive proof that SD creep dominates deformation at fast strain rates and low temperature. Furthermore, stress transients following strain-rate changes under SD creep are observed to decay exponentially with strain. A new graphical construction is proposed for the analysis and prediction of creep transients. This construction predicts the relative size of creep transients under SD creep from the relative size of changes in an applied strain rate or stress. This construction reveals the relative size of creep transients under SD creep to be independent of temperature; temperature dependence resides in the “steady-state” creep behavior to which transients are related.