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

Abstract

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, 9 wt% Mn is added to Cu-31Zn alloy. In this research, Cu-31Zn-9Mn was fabricated by gravity casting and homogenized at 800 ℃ for 2 h. Furthermore, the alloy was cold-rolled with 20, 40, and 70% deformation. Samples with 70% deformation then annealed at 300, 400, and 600 ℃ for 30 min. 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 30 min caused decreasing hardness (201, 128, and 171 HV) due to the recovery phenomenon, recrystallization (d grain ∼ 5 μm), and grain growth (d grain ∼ 40 μm), 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.