Effect of Cold Rolling and Annealing Temperature on the Characteristics of Cu-28Zn-3.2Mn Alloy

Common material for bullet shell is cartridge brass which contains 26-32 wt. % Zn. In the deep drawing process, problems are typically found, such as cracking and tearing, due to low ductility. Therefore, manganese is added to cartridge brass to increase its ductility. In this study, Cu-28Zn alloy with addition of 3.2 wt. % Mn was fabricated by gravity casting. As cast samples were homogenized at 800 °C for 2 hours. Afterwards, the specimens were cold-rolled with deformation of 20, 40, and 70 %. The 70 % cold-rolled samples were subsequently annealed at 350, 400, and 450 °C for 15 minutes. Samples underwent characterizations by microstructure analysis using optical microscope and Scanning Electron Microscope (SEM) - Energy Dispersive Spectroscopy (EDS), and Vickers microhardness testing. The results showed that higher degree of deformation led to more elongated grains with increasing values of L/D ratio, and higher hardness. Annealing at 350 °C for 15 min did not change the deformed microstructures which indicated the stage of recovery and stress relieve. Meanwhile, higher annealing temperatures of 400 and 450 °C led to recrystallization and grain growth, respectively. Hardness declined with the increase in annealing temperature. Mn increases the hardness and recrystallization temperature.