High-strength and free-cutting silicon brasses designed via the zinc equivalent rule

This study reports on the formation of high-strength and free-cutting silicon brasses designed and adjusted via the zinc equivalent rule by adding Pb replacers (Si and Al elements). Microstructure analysis indicates that phase components of the designed silicon brasses transform from α+β to β and further to β+γ with the increased zinc equivalent induced by increased Si and Al contents, respectively. Meanwhile, many ultrafine intermetallic compound particles are distributed along the grain boundaries of the α and β phases and embedded into the β-phase matrix along with high densities of nanoscale intermetallic compounds distributed in the β-phase matrix close to the grain boundaries. With the increased zinc equivalent, β-phase microhardness and Brinell hardness of the designed silicon brasses increase gradually accompanied by an increase in ultimate tensile strength and a decrease in elongation. Evaluation of chip morphology and machining surface quality imply that α+β brass has good abilities for chip breakage and free-cutting machinability. These results provide significant insight into the microstructural design of high-strength and free-cutting brass alloys.