Effect of Co addition on hardness and electrical conductivity of Cu–Si alloys

High-strength and high-conductivity Cu alloys are widely required in railway and lead frames. As a conventional element, Si reduces the electrical conductivity of Cu alloys significantly. In this work, Co is introduced into Cu–Si alloys for improving the mechanical and electrical properties. The results show that the Co-containing alloy possesses much higher hardness and conductivity than the Co-free alloys. The added Co reacts with Si to produce high density of CoSi nanoprecipitates that have a semi-coherent interface with the Cu matrix in the aged Cu–Co–Si alloy. The presence of CoSi nanoprecipitates is sufficiently verified by X-ray, energy-dispersive spectrometer and electron diffraction pattern. The formation of CoSi nanoprecipitates can pin dislocation motion, prevent the recrystallization and reduce the Si solute concentration in the Cu matrix. The effects of precipitate hardening and precipitation purification from CoSi phase result in the better performance of the aged Co-containing alloy than the Co-free alloys. The success in Cu–Co–Si alloys opens a door to overcome the disadvantage of Si alloying in Cu-based alloys.