M.A. Khan, D.E.C. Lobo, P. Kang
George Mason University,
United States
Keywords: Al-C covetics, laser manufacturing, corrosion behavior, Tafel curve, electrochemical impedance spectroscopy
Summary:
Covetics are emerging composite materials fabricated by embedding carbon, particularly graphene in the metal matrix. The unique properties of graphene reinforce the electrical, mechanical, and chemical properties of the fabricated composites, such as the Aluminum-Carbon (Al-C) Covetics. Despite rapidly growing research on Covetics, the corrosion behavior of Al-C Covetics is rarely discussed in the literature, especially the corrosion mechanism. Therefore, this study aims to investigate the corrosion properties of Al-C Covetics using Potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) to unveil the dissolution behavior and governing corrosion mechanism of Al-C Covetics compared with as-received Al. Before Covetics fabrication and corrosion experiments, the as-received Al substrates were ultrasonically cleaned in Ethanol and deionized water, respectively for 5 min each, to remove any contaminants. In contrast, the fabricated Al-C Covetics substrates were directly used for corrosion experiments. All the electrochemical tests were conducted in 1% NaCl electrolyte at room temperature with a 0.36 cm2 area of substrate exposed to the electrolyte. The as-received Al or Al-Covetics as a working electrode, Ag/AgCl as a reference electrode, and graphite sheet as a counter electrode were fixed in a reaction cell and driven by the 600+ Gamry Potentiostat. At first, the Open Circuit Potential (OCP) of the electrochemical cell was monitored for an hour to ensure the stability of the working system. Subsequently, the EIS was performed over the 0.1 to 100,000 Hz frequency range. The cyclic polarization tests obtained the potentiodynamic response of the working system from -0.5 V to an apex voltage of 1.5 V with an automatically sweeping applied voltage. Each electrochemical corrosion experiment was repeated three times while keeping the electrode gap and Potentiostat configuration constant which significantly improved the experimental accuracy. The OCP results verified the stability of the electrochemical cell. The Tafel curve obtained by plotting sweeping voltage vs current was extrapolated for the quantification of electrochemical corrosion parameters such as the corrosion potential (Ecorr), the pitting potential (Epit), and the corrosion current density (Icorr). The Ecorr determines the corrosion initiation potentials, Epit determines the potential at which pits are formed on the substrate, while the Icorr is a measure of corrosion rate under given conditions. The Nyquist plot between real and imaginary impedance determined the corrosion response of as-received Al and Al-C Covetics at different frequencies. An Electrical Equivalent Circuit model was used for fitting the Nyquist data and to quantify the corrosion parameters. In conclusion, the corrosion properties and the dissolution mechanism of Al-C Covetics were investigated which brings to light an important aspect of the emerging material for potential metallurgical applications in different fields such as defense, aerospace, and automotive.