Influence of Minor Aluminum Addition on the Superplastic Deformation of a Microduplex Cu-Zn Alloy

High residual porosity in superplastically deformed brass carries the risk of reducing the mechanical properties. Multicomponent brasses demonstrate lower residual porosity, associated with a lower grain size and more effective accommodation of grain boundary sliding. In this paper, the microstructural evolution of the surface and bulk structure of the binary brass and aluminum-bearing brass during steady-state superplastic deformation is compared. After superplastic deformation, dislocation pile-ups and dislocation walls are revealed in the α grains of both alloys, indicating the activation of the dislocation slip/creep mechanism. It is shown that aluminum reduces the contribution of grain boundary sliding along the phase boundaries from ~75 to ~30% and causes strain localization in the β-phase region with the formation of ultrafine grains with the size below ~300 nm as a result of dynamic recrystallization. Alloying with 0.4% Al reduces the flow stress by 20%, increases the relative elongation by a factor of 1.5, and decreases the fraction of residual porosity by a factor of 3. This leads to a much lower loss of room temperature strength in superplastically deformed alloys.