Effect of Short Heat Treatments on the Microstructural Evolution and Hardness of Thixoformed Graphene Reinforced Aluminium Composites

Abstract

Aluminium metal matrix composites are increasingly being used in numerous industries due to their lightweight nature and high strength. The incorporation of graphene into aluminium metal matrix composites has garnered significant interest owing to graphene's capacity to enhance numerous properties concurrently. Hence, this study aimed to fabricate a 0.3 wt.% graphene nanoplatelets reinforced A356 alloy (GNP-A356) composite through stir casting followed by thixoforming and short T6 heat treatment processes. It also evaluated the microstructure and mechanical properties of GNP-A356 after the thixoforming process and short T6 heat treatment. The microstructure of alloy and composite was confirmed by optical microstructure, field emission scanning electron microscopy images, and X-ray diffraction. Microstructure investigations demonstrate the impact of the stirring process on the structural transformation of the 𝛼-Al phase from the dendritic into a rosette-like and globular-like structure. The result also indicated that there was a transformation of eutectic silicon from the shape of a needle-like to spheroid structure after a short heat treatment, showing the efficiency of T6 heat treatment with a shorter time of solution treatment and ageing. Moreover, the increase in relative density and addition of reinforcement led to a significant increment in hardness. The result shows the hardness improved by 35.77% and 77.8% for as-cast and heat-treated composites, respectively, compared to A356 alloy.