Microstructural characterization of Al4C3 in aluminum–graphite composite prepared by electron-beam melting

We prepared graphite-infused aluminum composites by electron-beam vacuum melting and electromagnetic stirring with 0% and 4 wt% graphite addition. Bulk density of 2.69 g/cm3 was measured for samples with 0% graphite addition (AlCv0) and 2.66 g/cm3 for samples with 4 wt% graphite addition (AlCv4). Both are > 99% of their theoretical values. X-ray diffraction indicated that AlCv0 is phase pure, while the AlCv4 sample is a composite consisting of aluminum, Al4C3, and graphite. Electron microscopy and energy-dispersive X-ray spectroscopy revealed pockets of carbon-rich phase of 10–50 μm in sizes dispersed in the Al matrix in AlCv4. Scanning transmission electron microscopy showed that Al4C3 crystallites of 1–2 μm sizes are mostly located near the outer shell of the pockets of carbon-rich phase and with undissolved graphite at the center. Thermal conductivity of 107.8 W/m K was measured for the AlCv4 and 226.7 W/m K for the AlCv0. Our work demonstrated the feasibility of producing pore-free high-density graphite-infused aluminum composite materials by electron-beam melting and electromagnetic stirring in vacuum.