Mechanical Properties of Copper Sulfide-Dispersed Lead-Free Bronze

Abstract

Microstructure, tensile properties and Vickers hardness of the copper sulfide (Cu₂S)-dispersed bronze produced by adding MoS₂ to molten bronze consisting of Cu and Sn were examined. The amount of Cu₂S and the number of casting defects increase with the amount of added MoS₂. The Vickers hardness of Cu₂S-dispersed bronze increases with the amount of added MoS₂. This is because the solid-solution hardening owing to Mo and the hardening due to the dispersion of Cu₂S are superior to the softening due to casting defects. The tensile strength of Cu₂S-dispersed bronze decreases with increasing amount of added MoS₂. This is because the softening due to casting defects outweights the solid-solution hardening due to Mo and the strengthening due to the dispersion of Cu₂S. The fracture elongation of Cu₂S-dispersed bronze decreases with the amount of added MoS₂. This is because the number of casting defects increases and Cu₂S acts as a nucleus of voids. To produce Pb-free bronze having excellent machinability and mechanical properties equivalent to those of CAC406 containing Pb and CAC902 containing Bi, adequate control of the amount and size of Cu₂S and the number of casting defects is of great importance.