Microstructure and properties of high-fraction graphite nanoflakes/6061Al matrix composites fabricated via spark plasma sintering

Abstract 30–50 wt.% graphite nanoflakes (GNFs)/6061Al matrix composites were fabricated via spark plasma sintering (SPS) at 610 °C. The effects of the sintering pressure and GNF content on the microstructure and properties of the composites were investigated. The results indicated that interfacial reactions were inhibited during SPS because no Al4C3 was detected. Moreover, the agglomeration of the GNFs increased, and the distribution orientation of the GNFs decreased with increasing the GNF content. The relative density, bending strength, and coefficient of thermal expansion (CTE) of the composites decreased, while the thermal conductivity (TC) in the X−Y direction increased. As the sintering pressure increased, the GNFs deagglomerated and were distributed preferentially in the X−Y direction, which increased the relative density, bending strength and TC, and decreased the CTE of the composites. The 50wt.%GNFs/6061Al matrix composite sintered at 610 °C under 55 MPa demonstrated the best performance, i.e., bending strength of 72 MPa, TC and CTE (RT−100 °C) of 254 W/(m·K) and 8.5×10−6 K−1 in the X−Y direction, and 55 W/(m·K) and 9.7×10−6 K−1 in the Z direction, respectively.