Synergetic Effect of Discontinuous Carbon Fibers and Graphite Flakes on Thermo-Mechanical Properties of Aluminum Matrix Composites Fabricated by Solid–Liquid Phase Sintering

Abstract

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.

From 1D to 2D arrangements of graphite flakes in an aluminium matrix composite: Impact on thermal properties

“…Regarding thermal matching, the Gf also has high anisotropy in CTE (-1 × 10 −6 /K in-plane, 28 × 10 −6 /K out-of-plane [17]). However, it was reported in the aligned Gf/Al composite that the overall CTE along the base plane of graphite merely decreases from 25 × 10 −6 /K to 22 × 10 −6 /K when the volume fraction of Gf increases up to 50% [9].…”

Metal Matrix Composite in Heat Sink Application: Reinforcement, Processing, and Properties

“…Recently, hybridizing AMCs with secondary reinforcements to mitigate the side effects of adding primary reinforcements [ 103 , 139 , 140 , 141 , 142 ] and to make the resulting composite more suitable for the intended application has gained popularity. Shu et al [ 103 ] hybridized aluminum matrix with Ti and B 4 C to form TiC x -TiB 2 /Al composites.…”

“…Molina et al [ 139 ] reported a thermal conductivity of 390 Wm −1 K −1 by reinforcing Al-12wt%Si alloy matrix with graphite flakes and SiC particles. Chamroune et al [ 140 ] hybridized aluminum matrix with graphite flakes and carbon fibers, featuring an in-plane thermal conductivity of 410 Wm −1 K −1 with in-plane and through plane coefficients of thermal expansion of 15 × 10 −6 K −1 and 2.4 × 10 −6 K −1 , respectively, using solid-liquid sintering. In another study, Peng et al [ 141 ] reinforced graphite flakes and carbon fibers in aluminum matrix, yielding a thermal conductivity of 402 Wm −1 K −1 .…”

“…It can be observed that, in general, diamond reinforcement is effective in significantly reducing the coefficient of thermal expansion as compared to other reinforcements [ 116 , 119 , 123 ]. Graphite reinforcement induced a very large anisotropy in the coefficient of thermal expansion of aluminum, ranging from a negative [ 127 , 129 ] to unacceptably high [ 129 , 140 ] values. On the other hand, hybrid AMCs present a desired reduction in the coefficient of thermal expansion [ 142 , 143 ].…”

“…Graphite as reinforcement in copper presents acceptable thermal properties only in the direction perpendicular to the pressing direction [ 44 , 70 ]. Graphite reinforcement induced a very large anisotropy in the coefficient of thermal expansion of aluminum, ranging from negative [ 127 , 129 ] to unacceptably high [ 129 , 140 ] values. An acceptable thermal performance is observed by reinforcing CNTs in copper by electrodeposition [ 75 ].…”