Hardness and microstructure of 44%Cu-27% Zn-23%Nb brass with various holding time during the precipitation hardening process

Abstract

In non-ferrous metals, solution annealing is often known as the method of precipitation hardening. Precipitation hardening is a heat treatment process which consists of two heating processes: the solid solution process and precipitation hardening/ageing. In this study, a heat treatment was carried out using precipitation hardening method with solution treatment at a temperature of 800 °C for 5 hours and precipitation hardening was performed at a temperature of 300 °C with holding time variations of 15 minutes, 30 minutes, and 45 minutes. After, the hardness and microstructure testing was carried out to determine the mechanical properties. This research aimed to obtain the optimal holding time during precipitation hardening method of 44%Cu-27%Zn-23% Nb Zn brass material. The improvement of mechanical properties, especially hardness value, occurred in the brass specimen with a holding time of 15 minutes. The brass’s microstructure with precipitation hardening treatment did not change, namely the α + β phase. The changes occurred in the α phase size, decreasing and the emergence of a new β phase in a small size. Thus heat treatment create new precipitate phase namely γ phase as the result of 22% Nb content. As the holding time increases, the size of precipitate will grow larger become the coarse precipitate and reduce the mechanical properties of the specimen especially hardness value.