Establishment of a facile technique to fabricate bulk AA6061/CNT composite with improved mechanical properties using combined stir-casting and squeeze-casting

Abstract

Three dispersion techniques were investigated for fabricating AA6061–0.5 wt% CNT composites by combined stir-casting and squeeze-casting - direct drop of CNT (DD), mixed Al and CNT pellet drop (PD), and direct drop of ultrasonicated CNT (USDD). Al-20Mg alloy was added to enhance CNT wettability. The PD samples resulted in the highest retention of CNTs in the matrix along with a uniform distribution, confirmed by detailed transmission electron microscope analysis. The selected area electron diffraction pattern and X-ray diffraction confirmed the formation of Mg2Si. The hardness of all composite samples increased significantly over AA6061, predominantly due to a reduction in crystallite size and an increase in dislocation density. The best combination of tensile properties was achieved in the PD composite, yielding an improvement of ultimate tensile strength and yield strength by 40% and 33%, respectively, compared to as-cast AA6061 without sacrificing the ductility. Well-developed serrations were observed in the stress-strain plots of the samples, which have been attributed to the pinning-unpinning action of mobile dislocations by the Mg solute atoms. The fracture surface of the PD composite displays features of ductile fracture along with CNT bridging and rupture, confirming the presence of a strong interface and effective load transfer strengthening.