Solid-State Additive Manufacturing of Al-Si-Mg-Graphene Metal Matrix Composites

Aluminum Alloy 6061 mixed with graphene nanoplatelets (GNPs) were additively friction stir deposited (AFS-D) into a metal matrix composite (MMC). AFS-D is a solid-state process whereupon feedstock is passed through a rotating, hollow tool in which sequential layers are built onto each other. The frictional rotation provides a thermomechanical process to mix materials together into fully dense structures. In this work, we fed premixed 0.25 to 2 wt.% GNPs with aluminum 6061 powder. The resulting depositions were characterized with X-ray diffraction, optical and electron microscopy, and Raman spectroscopy techniques. The GNPs were found to be uniformly distributed in the microstructure. Minor differences in particle dispersion between the retreating and advancing sides of tool rotation were observed and quantified. The rotation of the tool was also noted to refine the GNP size distribution. Raman spectroscopy confirmed the graphitic nature of the GNPs in the matrix after deposition as well as a noted increase in its structural disorder. The hardness with respect to the GNP dispersion for in plane and out of plane deposited directions was measured. Finally, the tensile strength of the MMC was measured and correlated to the GNP content.