EFFECT OF T6 HEAT TREATMENT ON MICROSTRUCTURE AND HARDNESS PROPERTIES OF THIXOFORMED GRAPHENE-REINFORCED A356 COMPOSITES

Abstract

This study reports the development of graphene nanoplatelets reinforced A356 alloy matrix composites. In this investigation, a graphene nanoplatelet reinforced A356 alloy matrix composite was fabricated using stir casting and thixoforming processing, followed by T6 heat treatment. The microstructure and hardness characteristics of alloys and composites were analyzed using optical microstructure, field emission scanning electron microscopy, and microhardness testing. The outcomes show that mechanical stir casting can produce a non-dendritic structure in the composite. The microhardness of cast composites increased by 35.8% from the base alloy sample due to the graphene addition to the base alloy, which also resulted in grain refinement in the structure of the composite. The microhardness of composites is improved by 51.4 % and 70.5 %, compared to the A356 alloy after undergoing the thixoforming process and T6 heat treatment. The field emission scanning electron microscopy shows the coarsened eutectic Si particles, and the Si particles become more spheroids after the T6 heat treatment. The thixoformed composite also shows an increase in density and less porosity after the T6 heat treatment compared to the base alloy and cast composite. The subsequent T6 heat treatment technique significantly enhanced the composite hardness owing to the incorporation of graphene and spheroidization of eutectic Si particles.