Effect of multiple micro channel reinforcement filling strategy on Al6061-graphene nanocomposite fabricated through friction stir processing

Graphene nanoplatelets (GNP) reinforced Al6061 surface composites were successfully fabricated by multiple micro channel reinforcement filling (MMCRF) strategy during multi-pass friction stir processing (FSP), aiming to improve the GNP distribution in the Al6061 matrix, increasing surface hardness and strength of the Al6061 alloy. Microstructure observations indicated that the GNP's are more homogeneously distributed and randomly oriented in the Al matrix when fabricated through MMCRF strategy as compared to single channel reinforcement filling (SCRF). Further, excellent interfacial bonding without any reaction product due to the severe plastic deformation by FSP is observed between GNP and Al matrix by TEM analysis. Thermal analysis during FSP reveals similar to 18% higher peak temperature in composite fabricated by MMCRF strategy compared to SCRF strategy whereas axial force observed during FSP is low and more uniform with MMCRF as compared to SCRF strategy. Nano-mechanical tests showed that the hardness of the composite increased by similar to 84% when impregnating reinforcement through MMCRF strategy as compared to SCRF whereas the ultimate tensile strength (UTS) of composites fabricated by MMCRF is similar to 28% higher than the UTS of composite fabricated through SCRF strategy. Grain refinement and shear lag model are identified and verified as the primary strengthening mechanism of the composite fabricated through MMCRF. Raman spectroscopy and residual stress/phase analysis using X-Ray diffraction corroborate the experimental observations.