Effect of misch metal on elevated temperature tensile ductility of the Cu-Zn-Bi alloy

Abstract

Cu-Zn-Bi alloy has been regarded as the most promising substitute for free-cutting leaded brass (Cu-Zn-Pb), which contains over 0.5 wt pct of hazardous Pb for the machinability of Cu. The Bi in Cu-Zn-Bi tertiary alloys, however, embrittles Cu because of its tendency to form a Bi film along phase boundaries, prohibiting the hot rolling over 271.4 °C, which is the melting temperature of BI. Misch (Ms) metal, which is a mixture of Ce, La, Nd, etc., can form a variety of stoichiometric compounds with Bi, and may reduce the Bi film formation along α and β phase boundaries. In the present study, the effect of Ms metal on tensile behavior of Cu-Zn-Bi alloys was examined at room temperature and 300 °C to quantify the host rollability. It was found that elevated temperature tensile elongation of Cu-Zn-Bi alloy was significantly improved, while the Bi film along phase boundaries was greatly inhibited, with the addition of 0.1 wt pct Ms metal. It was also noted that the Bi film along phase boundaries was greatly inhibited probably due to the formation of intermetallic compound between Ms metal and Bi. The addition of 0.3 wt pct Ms metal was, however, not beneficial to the tensile ductility of Cu-Zn-Bi alloy at 300 °C. Since the solubility of Ms metal in Cu is very low, the Ms metal, added ove r0.1 wt. pct, may therefore remain as impurities. These impurities would eventually reduce the tensile elongation of Cu-Zn-Bi alloy at room and particularly high temperatures.