Optimisation of mechanical stir casting parameters for fabrication of carbon nanotubes–aluminium alloy composite through Taguchi method

Abstract

The liquid metallurgical process route for synthesis of multiwalled carbon nanotube–A356 aluminium alloy (MWCNT-A356) composite is suitable for intricate designs and bulk production. In this work, MWCNT-CNT was fabricated through mechanical stir casting followed by thixoforming and modified by T6 (MT6) heat treatment. Hence, the optimisation and effect of variables such as amount of CNT, amount of wettability agent of Mg and mechanical stirring duration were investigated using a robust design of experiment (DOE), namely, Taguchi method, with two factorial levels. The signal-to-noise (S/N) ratio (‘larger is better’), hardness and ultimate tensile strength (UTS) were used as response variables. Results showed that the optimum hardness and UTS values of 106.4 HV and 277.0 MPa, respectively, were obtained from the nanoncomposite subjected to DOE run 4 and containing 0.5 wt.% MWCNT, 0.5 wt.% Mg and 10 min of mechanical stirring. The hardness (76.3%) and UTS (108.4%) improved compared with those of the as-cast A356 alloy. The transformation of the microstructures and the porosity of the as-cast after thixoforming and MT6 modification were also discussed. This work demonstrated the optimised mechanical stir casting parameters for MWCNT-A356 fabrication and the enhanced mechanical properties achieved by thixoforming and heat treatment. Keywords: Thixoforming, Metal matrix composite, Multiwalled carbon nanotube, A356 alloy