Analysis of the microstructure evolution, enhanced hardness and electrical conductivity of T6 heat-treated A319/graphene composites

In this research, the microstructure evolution, hardness and electrical conductivity of a T6 heat-treated A319/graphene nanoplatelets (GNP) composite were investigated. Microstructural analysis was carried out using an optical microscope and a scanning electron microscope equipped with energy-dispersive X-ray spectroscopy (EDS). Transmission electron microscopy was also performed using brightfield and high-angle annular dark-field detectors in combination with EDS. Hardness and electrical conductivity measurements were performed through Vickers microhardness testing and eddy current testing, respectively. Graphene nanoplatelets led to a uniform dispersion of the microstructure, enabling more effective solution heat treatment of the composites. It is proposed that GNPs facilitate increased dissolution of Al2Cu, leading to improved kinetics for aging and accelerated precipitation of θ’-Al2Cu. This mechanism is attributed to the CTE mismatch between graphene and Al, which enhances Cu diffusion rate. Additionally, spheroidization of eutectic Si was observed during heat treatment. The evolution in microstructure correlated well with hardness and electrical conductivity results. The maximum hardness was measured at 111.43 ± 3.35 HV (34% increase) for the A319/0.1GNP composite aged at 250 °C while the maximum electrical conductivity was measured at 35.92%IACS (32% increase) for the A319/0.2GNP composite for the same heat treatment condition. The work demonstrates that the heat treatment process parameters can be optimized for enhancement of the properties of aluminum/graphene composites.