Microstructure and properties of copper coated graphene nanoplates reinforced Al matrix composites developed by low temperature ball milling

Copper nanoparticles coated graphene nanoplates reinforced Al (Cu-GNPs/Al) matrix composites were fabricated by the combination of low temperature ball milling (LTBM) and subsequent hot extrusion process. The as-obtained composite with 2.5 wt% Cu-GNPs showed excellent comprehensive properties, i.e. the tensile strength (402 MPa) is 130% higher than that of monolithic Al, meanwhile, the fracture elongation over 10% was maintained. It was found that compared with room temperature ball milling, the LTBM processing could improve the dispersion of graphene in the matrix remarkably and thus enhance the strength of the composites substantially. The introduction of Cu-GNPs weakened the < 111 > fiber texture of the Al matrix but refined grains as well as reduced the thermal expansion coefficient of the composites. The coated Cu on the GNPs enriched at the interface and inhibited the severe interfacial reaction, which would enable the structural integrity retention of GNPs and improved the interfacial bonding strength and thus be very favorable for the load transfer between GNPs and Al matrix. In addition, two sizes of GNPs were found in the composites due to the ball milling processing, the larger-sized GNPs contributed a lot to the load transfer while the smaller ones contributed more to the Orowan strengthening.