Effects of grain size and strain rate on ductility of Cu-30 mass%Zn alloy at 673 K

The purpose of this paper is to consider the effects of initial grain size and strain rate on the ductile behavior of a Cu-30 mass%Zn alloy under high temperature deformation, and the related microstructural changes associate d with it. Salt bath tensile tests on specimens with initial grain sizes of 12, 22 and 45 mu m were studied under various strain rates from 3.3 x 10(- 5) s(-1) to 2.0 x 10(-2) s(-1) at 673 K. The elongation and the fractured o ptical microstructures of the specimens were investigated. Maximum elongati on of the specimens occurred at an initial grain size of 12 mu m under a st rain rate of 6.7 x 10(-4) s(-1). In this case most of the microstructure of the specimens changed to a fine dynamic recrystallized structure. The poss ibility that the principal deformation mechanism of the fine structure is g rain boundary sliding, similar to superplasticity should be considered. As a consequence, the specimens exhibit high elongation. Under the lower strai n rates, dynamic recrystallization occurred, i.e. dynamic recrystallized fi ne grains were observed. The dynamic recrystallized grains grew after the d eformation, and thus the elongation of the specimens decreased. By increasi ng the strain rate or the initial grain size, the slight dynamic recrystall ized structure occurred around the initial grain boundary. The dynamic recr ystallized structure zones are geometrically softer than the initial grains , and thus basal slip is likely to be the dominant mechanism. Therefore the specimens show low elongation and shear fracture. Furthermore, the extent of ductility depends on the shape of the cavity which is induced by the dif ferences of the initial grain size and the strain rate.