Electroplating of Nano-Structured Alumina Reinforced Copper Composite Coatings

Abstract

Copper, as the first metal ever used by humans, is one of the most important metals in the world. Copper has excellent conductivity of electricity, which is only second to silver; and combined with high thermal conductivity, reasonable strength, good ductility and corrosion resistance, copper and its alloys have been widely used in electrical industry, such as electrical transmission and contacts in switches. As an efficient electrical contact, it has to successfully close the circuit, carry the current without overheating and break the current without damaging the switch through many thousands cycles during its lifetime. Copper has high electrical and thermal conductivities. However, its hardness and wear resistance are not high. To improve the mechanical properties, including microhardness and wear resistance, of copper for electrical contacting applications, copper based composite coatings can be applied by electroplating. In this research, Cu-Al2O3 nano-particle composite coatings were prepared, where Al2O3 nano-particles were introduced in a sol form. By adding Al2O3 sol, the agglomeration of Al2O3 nano-particles could be prevented; and so to ensure the homogeneity of particle dispersion in the electrolyte. The influence of sol concentration and some other electroplating parameters on the mechanical properties of Cu-Al2O3 composite coatings was investigated. Pure copper coatings were firstly prepared under varying electroplating parameters. The optimum conditions were found to be 50 mA/cm2 and 10 min; and under these conditions, Cu-Al2O3 composite coatings were prepared with varying Al2O3 sol concentration in the plating bath. It was observed that by introducing Al2O3 sol, the microhardness was increased by 25%; and the wear resistance was greatly improved by 85%. The presence of Al2O3 nanoparticles in the composite coatings was confirmed by XRF spectra. However, as the amount of Al2O3 nano-particles in the copper matrix was very small, the accurate concentration could not be calculated and needed further investigations. Finally, the mechanisms of mechanical properties enhancement were discussed based on the microstructure studies.