Flow stress and recrystallisation during hot deformation of Cu-9%Sn alloys

Compression tests were carried out on two compositions of Cu-Sn bronze: Cu- 9.2Sn and Cu-9.1Sn-0.26Zn (wt-%). The experiments were performed at tempera tures from ambient up to 750 degrees C and at nominal (initial) strain rate s in the range 10(-3) to 10(-1) s(-1). The measured data were converted int o true stress-true strain curves; these displayed yield drops as well as si ngle peaks (or maxima) at higher temperatures and lower strain rates. The m ean rate sensitivity applicable to the curves was 0.25. Optical metallograp hy indicated that dynamic recrystallisation of the 'grain refinement' type was taking place at the higher temperatures and proceeded by necklace forma tion. Electron backscattered diffraction measurements were also carried out ; these revealed that twinning plays an important role in these materials. The present results show that the pl ogress of recrystallisation is conside rably slower than in OFHC copper and that the recrystallised grain size is appreciably finer. These observations, taken together, all indicate that th e high temperature flow behaviour of the tin bronzes is controlled by solut e drag and is not of the conventional 'pure metal' type.