Hybrid Electrodeposition of Ag-Graphene Composite Films on Cu Alloys for High-Conductive and Wear-Resistive Automotive Connectors

Abstract

In recent years, plug-in hybrid electric vehicles (PHEV) and plug-in hybrid vehicles (PHV) have become popular due to depletion of fossil fuels. At the tip of the wire harness, which is said to be the nerve of automobiles, there are numerous terminal connectors that are connected to various electronic devices, and the demand for their reliability is every increasing with the progress of PHEVs and PHVs. Considering the conductivity and heat generation, Cu alloys that plated with a highly conductive Ag film are commonly used. However, in addition to the problem of soaring costs due to the increased use of noble Ag, which is a, there is an important problem that the wear resistance of Ag is insufficient because of its adhesiveness during sliding and/or its soft nature, which has been unsolved yet.In this study, we are aimed at fabricating a novel Ag-graphene composite films on Cu alloys though a facile hybrid electrodeposition. Here, graphene is used to function as an effective solid lubricant, while maintaining the conductivity of Ag matrix plating films that are indispensable to various automotive connectors. A commercial Cu alloy sheet was used as the base material. Graphene was produced by electrolytically exfoliating Graphite. A cyan-free Ag plating solution containing home-made graphene nano-flakes was adopted in electrodeposition. The thickness of the deposited films was designed to be 5 mm and controlled by depositing conditions. The resultant specimens were investigated by FE-SEM, EDX, GD-OES, Raman spectroscopy. The properties such as hardness, resistivity, and wear resistance were also evaluated.Fig.1 shows the surface FE-SEM images of as-deposited pure Ag and Ag-graphene films. Both the pure Ag and the Ag-graphene composite film were smooth, consisting of nano-sized fine particles. It can be seen in the Ag-graphene composite film that, there were some areas where the particle size was slightly larger, and moreover, a hazy film-like material was observed on them, which was examined as C by EDS analysis. Fig. 2 shows the Raman spectroscopic measurement results of the pure Ag film and the Ag-graphene composite films. Compared to peak-less spectrum of pure Ag film, three typical peaks were detected in Ag-graphene composite film. The detected peaks are indexed to be D-band, G-band, and 2D-band from graphene, thus indicating the co-deposition of Ag and graphene flakes during the hybrid Ag electrodeposition and graphene electrophoretic deposition. Moreover, it was also found that the Ag-graphene composite films exhibited higher hardness and lower friction coefficient compared to the pure Ag film, thus confirming a promising candidate material for high-conductive and wear-resistive automotive connectors. Figure 1