The optimization of metal-matrix composite material is linked firstly with the intrinsic properties of the matrix and the reinforcement used and secondly with the reinforcement-matrix interfacial zone and the distribution/orientation of the reinforcement inside the metal-matrix. Flake powder metallurgy was used to fabricate graphite flake reinforced aluminum matrix (Al/GF) composites fabricated by vacuum hot pressing. Two types of aluminum powders morphology were used: spherical (AlS) and flake (AlF) powders. A higher thermal conductivity in the in-plane direction of the graphite flakes was obtained for Al/GF composite materials fabricated with aluminum flake powder. In addition to a better orientation of the GF in the flake aluminum matrix, a 3D puckered surface and plane surface are formed at the Al/GF interface in, respectively, AlS/GF and AlF/GF composite materials. Due to the morphology incompatibility between the graphite flakes and the spherical powder, the damaged inner structure of GF contributes to a limited enhancement of thermal conductivity in AlS/GF composite materials.

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This study focuses on the powder processing methodology (PPM) for the fabrication of metal matrix composite using Graphite flakes (Grf) reinforced Copper (Cu). The manufacturing route involved 1) a reductive treatment of Grf powder to purify and increase its quality, 2) the mixing of the Cu and the Grf (0 to 40 vol.%) powders with a fast and efficient resonant acoustic (RA) mixer, and finally 3) the cold and hot-pressing of composite powders. Comparison of PPM is made with literature and a usual method used in our laboratory. The quality of Grf after different steps was analyzed by Raman spectroscopy and phase compositions and microstructure of the composite materials were analyzed by XRD and SEM, respectively. It was shown that this new PPM demonstrated better composite structural and thermal properties even at low volume fraction of Grf with a maximum of 630 W.m-1 .K-1 obtained with 40 vol.% of Grf at 70 °C. This was possible thanks to our new PPM which allows getting lower defects in the Carbon lattice of Grf and oxygen content in the final composite materials.

Aluminum (Al) matrix composite materials reinforced with graphite flakes (GF) and pitch-based carbon fibers (CF) were fabricated by solid-liquid phase sintering with a small amount of Aluminum-Silicon eutectic alloy (Al-12wt%Si). The amount of Al-Si is optimized for a carbon content of 50 vol.% in order to achieve, in the plane of GF reinforcement, a higher thermal conductivity (TC) and a lower coefficient of thermal expansion (CTE) compared to identical composite material fabricated by conventional powder metallurgy route. Al/(GF+CF) composite materials were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray microscopy and X-ray tomography in order to highlight the distribution of the Al-Si liquid phase and the formation 2 of a carbon network in the aluminum matrix. A small amount of CF allows to control the through-plane CTE without affecting significantly the in-plane TC of the Al-C composites. The (GF+CF) mixture and the solid-liquid phase sintering allow to achieve a TC of 410 W/m.K (in-plane direction) and a CTE of 2.4×10-6 /K (trough-plane direction), which is, for example, applicable for lightweight heat sink material.

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