Effect of 9wt% Mn addition on cold rolling and annealing behaviour of Cu-31Zn alloy

The primary material to make bullet shell, cartridge brass (with 28-32% Zn), is required to have proper ductility and controlled recrystallization. These properties will reduce cracks when bullet shells are fabricated and deformed up to 70%. In order to increase ductility, 9wt% Mn is added to Cu-31Zn alloy. In this research, Cu-31Zn-9Mn was fabricated by gravity casting and homogenized at 800 for 2h. Furthermore, the alloy was cold-rolled with 20, 40, and 70% deformation. Samples with 70% deformation then annealed at 300, 400, and 600 for 30min. The results showed that the increments in deformation for 20, 40, dan 70% lead to second phase piping with L/T ratios of 4, 16, and 18, followed by the increment in hardness to 147, 171 and 205 HV, respectively. On the other hand, annealing treatment at 300, 400, and 600 for 30min caused decreasing hardness (201, 128, and 171 HV) due to the recovery phenomenon, recrystallization (d _grain∼5μm), and grain growth (d _grain∼40μm), respectively. In order to achieve complete recrystallization in a brass cartridge with the addition of Mn, higher annealing temperature or longer holding duration is required than that of the base Cu-Zn alloy.