INFLUENCE OF MINOR ALUMINUM ADDITION ON THE SUPERPLASTIC DEFORMATION OF A MICRODUPLEX CU-ZN ALLOY

Abstract

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 mechanisms of grain boundary sliding. In this paper, a comparison is made of microstructural evolution in the prepolished surface and in the bulk of duplex brass samples and brass samples with minor aluminum addition during steady-state superplastic deformation. After superplastic deformation, dislocation clusters and dislocation walls are revealed in the α-grains of both alloys, indicating the activation of the dislocation 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 ß-phase region with the formation of less than ~300-nm grains 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 amount of residual porosity by a factor of 3. This leads to a much lower loss of strength in superplastically deformed specimens at room temperature.