Effect of chemical composition and processing variables on the hot flow behavior of leaded brass alloys

Hot compression tests were carried out on CuZn39Pb2 and CuZn39Pb3 leaded brasses in the temperature range of 600-800 °C at strain rates of 0.001-1 s−1. The stress-strain curves at low temperatures were characterized by a single peak, while at high temperatures, the flow curves were characterized by a long plateau associated with dynamic recovery. The phase diagram of Cu-Zn-Pb system drawn by the Thermocalc software showed that increasing Pb could shift the phase border between α+β and β towards the Zn corner, thereby increasing the volume fraction of α at the deformation temperatures. Hot deformation at low temperatures, e.g., 600-700 °C, changed the strings of cornered α islands to more globularized discrete ones. However, the conventional dynamic recrystallization could not be observed. At 800 °C, fine α particles formed through dynamic recrystallization were coexistent with acicular ones formed through quenching of β from high temperatures. It was found that at low temperatures, e.g., below 700 °C-750 °C, Pb could contribute to avoiding flow localization in both alloys. At 800 °C, more Pb could dissolve into β leading to more tendency to flow localization. The results showed that at low temperatures, i.e., below 700 °C, both materials exhibited higher strength than that predicted by the law of mixture. At high temperatures, particularly beyond 700 °C, the predicted values of the law of mixture lay below the experimental flow stresses. This was attributed to the decrease in the volume fraction of α and more dissolution of Pb into β.