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Natural Graphite Reinforced Aluminum: A Cost/Performance Paradigm Changing Technology for High Heat Flux Thermal Management
Keywords: Thermal conductivity, Thermal expansion matching, Natural graphite reinforced Al
Low cost natural graphite platelet reinforced Al (AlGrp™) composites manufactured by net shape pressure infiltration casting are being produced for high heat flux thermal management with CTE matching. The in-plane CTE of AlGrp can be engineered from 4 ppm/K to 9 ppm/K with respective thermal conductivity values of ~850 W/mK to ~700 W/mK. Depending on the thermal needs and overall part design, the through thickness thermal conductivity can be improved from 30 W/mK to ~850 W/mK by in-situ forming inserts of AlGrp/MetGraf preforms for hot spot remediation and local engineering of CTE to match the semiconductor package. These AlGrp components are net-shape cast with a continuous skin of the matrix Al alloy or a thin skin of MetGraf which can be Ni or Ni/Au plated for solder die attach. Applications requiring greater mechanical strength and high thermal conductivity such as electronic chassis, enclosures and satellite structures have been co-infiltrated with high specific stiffness structural skins made from quasi-isotropic continuous graphite fiber. When structural skins are combined with “z” inserts™ for hot spot remediation and local CTE engineering, the overall hybridized AlGrp component creates a lightweight thermo-structural solution. Variations of this technology have utilized embedded cast-in cooling channels which extends the technology to large integrated systems. A thermal and mechanical database resulting from recent process improvements with ever increasing thermal conductivity will be presented. Also presented will be preliminary results from recent investigations of natural graphite reinforced copper composites (aka CuGr). The performance of natural graphite platelets in aluminum will be analyzed with respect to Al matrix composites reinforced with similar sized machining scrap from the best grades of synthetic graphite (e.g. APG). The intrinsic thermal conductivity of natural graphite will be determined by comparison of properties of synthetic and natural graphite reinforced Al composite systems.
James A. Cornie, CTO, Chairman
Metal Matrix Cast Composites
Waltham, MA

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