Microstructure and machinability of Zn-Cu-Mg-Al-RE zinc alloy

The microstructure and machinability of a self-developed Zn-Cu-Mg-Al-RE zinc-based alloy (to replace HPb 59-1 brass) under the cast, heat-treated and extruded conditions were investigated by optical microscope analysis, X-ray diffractrometry analysis, scanning electron microscope observation and energy spectrum analysis. The machinabilities of Zn-Cu-Mg-Al-RE zinc-based alloy under the three conditions were compared with that of HPb 59-1 brass. The results show that the white massive structure which is rare earth compound and of brittleness, distributing at grain boundaries discontinuously under the cast condition, is helpful for cutting, but it disappears under the extruded and heat-treated conditions. The matrix structure recrystallizes after extruded, and secondary recrystallization which refines the grain can be observed in the alloy after heat-treated. The machinability of the as-cast alloy is close to that of HPb 59-1 alloy, and it is higher than those of as-heat-treated and as-extruded alloys.