Superplastic behavior of coarse-grained aluminum alloys

In this paper we concentrate on the superplastic behavior and the microstructural evolution of two coarse-grained Al alloys: Al–4.4w/oMg and Al–4.4w/oMg–0.4w/oCu. The values for the strain rate sensitivity index and activation energy suggest that solute drag on dislocation motion is an important phenomenon. The plasticity of these materials is further enhanced by a reconstruction mechanism due to dynamic recovery and recrystallization. At temperatures lower than 450 °C and for strain rates up to 10−2 s−1 the main reconstruction mechanism can be described by dynamic recovery. The dynamic recovery compensates the strain hardening and the deformation takes place in a steady state like mode resulting in high values for the maximum tensile elongation (260% for Al–Mg and 320% for Al–Mg–Cu). The deformed microstructure is characterized by a lower value of the average grain size and an increased density of low angle grain boundaries as compared to the original materials. At higher strain rates dynamic recrystallization produces oscillations of the flow stress curves or a coarser microstructure.