Graphene-impregnated Al6061 nanocomposites: microstructural and micromachining study

Graphene nanoplatelet (GNP)-reinforced aluminum matrix nanocomposites have drawn interest in both industries and academia because of their superior mechanical properties, such as hardness and tensile strength. Despite these merits, GNP-reinforced composites are seldom utilized in industrial applications due to their low machinability. This article explores the microstructural, mechanical, and machining analysis of the Al6061/GNP-reinforced nanocomposite fabricated by bottom pouring stir casting. Microstructural characterization techniques such as scanning electron microscopy (SEM), X-ray diffraction, transmission electron microscopy, and Raman spectroscopy were performed to analyze the surface morphology, and mechanical properties were evaluated using micro- and nanohardness testing. The microstructure of GNP-based nanocomposite revealed Al–Fe–Cr intermetallic phases and GNP particle aggregation. The Al6061/GNPs nanocomposite showed a ~ 28% reduction in grain size attributed to the incorporation of GNPs, which impede the grain boundary movement. The Al6061/GNP nanocomposite showed 130% and 31% enhancement in nanohardness and microhardness, respectively, compared to the unreinforced stir-cast alloy. A mismatch in the coefficient of thermal expansion and load transfer from matrix to reinforcement was observed as the main strengthening mechanism. To assess machinability, micromilling experiments were conducted in dry conditions. Al6061/GNP-based microchannel showed lower burr formation, a smooth channel profile, and better dimensional accuracy than unreinforced stir-cast Al6061 alloy. Adhesion and abrasion were observed as major tool wear mechanisms during the micromilling of Al6061/GNP nanocomposite. Material removal mechanism and modification in the GNP structure after machining were analyzed.