Microstructural development of brass alloys with various Bi and Pb additions

In the study, using the gravity casting method, adding 1.52%Pb, 0.5%Bi, 1%Bi and 1.5%Bi into the brass (Cu-40%Zn) alloy. The microstructural changes from the Widmanstätten into the networked structures when Pb was added to 1.5%. The microstructure was an acicular Widmanstätten when Bi contents were 0.5% and 1% and it was a plate Widmanstätten when Bi contents were 1.5%. There were four kinds of precipitation morphologies of Bi particles. The precipitation morphologies of Bi particles can be divided into a globular (<1 μm), a disc (=1 μm), discontinuous massive (>1 μm), and continuous block structures (about 20∼30 μm). The Pb particles were embedded in the networked α phase and the Bi particles precipitated at the α/α and the α/β′ grain boundaries. The XRD analysis showed the high proportion of β′ phase with 0.5% Bi-brass and 1% Bi-brass and indicated a lower one with Pb-brass and 1.5% Bi-brass.