Consolidation of Free-Cutting Lead-Free Brass by Hot Extrusion and its Properties

摘要

In this study, attempts were made to develop a method for consolidating of 6-4 brass chips and producing a free-cutting, lead-free brass alloy. Because chips of a lead-free brass alloy are not available commercially, a 6-4 brass alloy was cast. Next, chips in shapes similar to those produced as scrap were prepared by machining a Cu-Zn ingot. Cu2S powder was added to the brass chips as an alternative to lead, and they were mixed. The mixture was compressed in a mold and directly consolidated as an extruded rod by hot extrusion at 773 K. After extrusion, results of tensile tests conducted to examine the mechanical properties of the extruded rods showed that the tensile strength and elongation decreased with the addition of Cu2S. Cross-sectional microstructure observation showed that the microstructure became dense with an increase in the extrusion ratio. Energy dispersive X-ray (EDX) analysis showed a sulfur-rich area in the rods with a low extrusion ratio. In contrast, sulfur dispersed homogeneously in rods at a high extrusion ratio. The density increased by increasing the extrusion ratio and decreased by the addition of Cu2S. The hardness of the specimens containing Cu2S increased with an increase in the extrusion ratio, while the hardness of the Cu2S-free rod was very low. A cutting resistance test and chip observation indicated that an increase in the amount of Cu2S additive improved the machinability. After extrusion, almost satisfactory extruded rods were obtained, while a non-bonded region was observed around the top of each extruded rod.