Abstract
A low-power solid-state additive manufacturing process termed additive friction stir deposition (AFS-D) successfully deposited a bulk 6061 aluminum alloy - 2.5 wt.% graphene nanoplatelet (GNP) metal matrix composite. Post-deposition, the build exhibited a macrostructure with undulating onion-ring-like patterns similar to friction stir welding features. Optical and scanning electron microscopy (SEM) observed GNPs distributed within and along grain boundaries with the GNPs reduced in widths from 4,000 µm (pre-deposit) to 200 nm (post-deposit) through this solid-state deposition process. Differences in particle dispersion between the retreating and advancing sides of deposited material were also observed and quantified. Raman spectroscopy confirmed the graphitic nature of the GNPs in the matrix after deposition, which also showed an increase in disorder in the GNPs. The fully dense deposition consisted of microhardness across the cross section, varying from 45 to 70 HV, where higher hardness was correlated to the location of the GNP dispersions.
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