Interfacial structure in AZ91 alloy composites reinforced by graphene nanosheets

Graphene nanosheets (GNS) are the promising nano-reinforcements to fabricate bulk graphene-metal composites due to their excellent mechanical properties and large yield. However, the effective synthesis of such bulk graphene reinforced magnesium (Mg) composites remains challenging because of the poor interfacial bonding and the aggregation of GNS. Here, GNS possessing about 12 at. % residual oxygen (similar to 7: 1 C/O ratio) was synthesized by a thermal reduction method. These residual oxygen in GNS is beneficial to increase the interfacial bonding between GNS and the matrix of alpha-Mg by MgO nanoparticles, which synthesized through the occurrence of a reaction between the residual oxygen and a-Mg in the composites. TEM analysis reveals that the in-situ synthesized MgO nanoparticles can significantly improve the interfacial bonding between GNS and a-Mg owing to the formation of semi-coherent interface of MgO/alpha-Mg and the distortion area bonding interface of GNS/MgO. By filling 0.5 wt. % of GNS, the yield strength and elongation of the composite increased by 76.2% and 24.3%, respectively as compared to the matrix alloy. The significant improvement in mechanical properties of the composites is mainly due to the grain refinement, strong interfacial bonding and dislocation strengthening. (C) 2017 Elsevier Ltd. All rights reserved.