Electroless plating on graphene (GNPs) for surface modification and composites applications

Introduction Carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs), are two of the most interesting carbon nanostructures (CNSs) usable as reinforcement in metal matrix composites material manufacturing because of their excellent mechanical properties. Aluminium and magnesium are the most studied light weight metals used as matrices in metal composites principally to their low density (respectively 2.7 g/cm3 and 1.7 g/cm3) and low melting temperature (around 660 °C for both metals). The improvement of mechanical properties of these structural metals allows to obtain environmental and technical benefits thanks to the possibility to reduce the global weight of different type of vehicles. However, carbon structures have a poor wettability with liquid aluminium and magnesium causing many technical problems during manufacturing process of composites. Nickel is one of the most used metals that exhibits a great affinity with aluminium and magnesium and it is successful used to the application of a functional coating onto the surface of the CNSs in order to improve their wettability by molten metal matrix. In this work, pure aluminium and magnesium alloy (AZ63) composites were produced with modified GNPs. Material and Methods GNPs were functionalized with coating through a new electroless pure nickel deposition using hydrazine instead of hypophosphite as reducting agent. Powder metallurgy method was applied for composites production: GNPs, modified with nickel, were mixed with aluminium or magnesium powders and then melted and casted in induction furnace with centrifugal casting system in inert atmosphere. Nickel effects on fillers-matrix interfaces was investigated by SEM and EDS analysis. Composites mechanical properties were evaluated by four-point flexural tests. Results An improvement of aluminium and magnesium alloy wettability on GNPs coated with nickel was shown and a better dispersion of fillers was exhibited compared to uncoated one. Discussion The coating of GNPs made with a nickel solution containing hydrazine than hypophosphite seems to modify significantly the GNPs metallic interface, moreover it allows to obtain a good dispersion of the reinforcements in the matrix avoiding formation of agglomerates.