2010 Volume 51 Issue 5 Pages 855-859
The aim of this paper was to produce a lead-free machinable brass dispersed with bismuth and graphite particles by powder metallurgy process. The effect of the machinable elements on the elongation and machinability of extruded materials was investigated. The Cu-40 mass%Zn (Cu-40Zn) brass powder with 0∼3.23 mass% bismuth additions were produced by rapid solidification process, having a mean particle size of 150 μm. It was found that bismuth were uniformly dispersed as the island of about 5 um in the brass powder matrix, and appeared at the brass powder surface after heat treatment over the melting point of bismuth. When 2.2 mass% or more bismuth was added, the quantity of bismuth appearing at the brass powder surface increased because of saturated quantity of bismuth elements in the brass powder. There were bismuth islands of tens of microns in the extruded brass with 2.2 mass% or more bismuth addition. These bismuth islands were depressed the elongation of extruded materials. The graphite particles with mean particle size of 5 μm were also used as raw powder. 0∼0.5 mass% graphite particles were mixed with the as-atomized brass powder by dry process. The elongation of the extruded brass alloy with both bismuth and graphite particles additions increased comparing with that of extruded brass with bismuth addition. The extruded brass using the as-atomized brass powder with 2.2 mass% bismuth and 0.5 mass% graphite particles indicated excellent machinability as well as the conventional leaded brass. Synergy effect of bismuth and graphite particles on the improvement of elongation and machinability of brass alloys was much useful compared with the brass containing only bismuth or graphite particles.
