Bismuth appears to have significant potential as a nontoxic alternative to lead for enhancing the machinability of alpha + beta brass because of similarity of features between lead and bismuth, e.g. low solubility for copper alloy and low melting point. It is reported that dispersing bismuth particles finely and uniformly, which means decreasing an average spacing of them, is effective on improvement in machinability of bismuth substituted lead free free-cutting brass. However bismuth particles in this alloy grow following to grain growth of alpha matrix because of the high wettability of bismuth at grain boundaries of alpha copper and so this alloy is inferior to leaded free-cutting brass in machinability. In this paper, the refinement of bismuth particles in Cu-Zn-Bi alloy was investigated. A refinement of matrix of this alloy by means of decreasing extrusion temperature made little effect on refinement of bismuth particles at low extrusion ratio. In consideration of spheroidized of bismuth particles in beta phase which decrease difference of surface energy against bismuth, this alloy has been extruded at high temperature during which matrix is only beta phase. As a result, refinement of bismuth particles in this alloy was achieved independent on extrusion ratio. And cutting chips of this alloy with fine bismuth particles were cut apart finer than of one with coarsened bismuth particles. Furthermore refinement of bismuth particles could not reduce the cutting resistance of this alloy as the same level of leaded free-cutting brass. It was deduced the difference of lubricity between bismuth and lead was involved in this case.
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