Effects of Graphite on the Corrosion Behavior of Aluminum-Graphite Composite in Sodium Chloride Solutions

A series of different aluminum-graphite composites (Al-Gr), namely pure Al, Al-1%Gr, Al-2%Gr, and Al-3%Gr, was fabricated. The surface of these composites was investigated using optical microscopy to examine the distribution of exfoliated graphite within aluminum. The corrosion behavior of the pure Al and Al-Gr composites after different immersion intervals in 3.5% NaCl solutions was carried out using cyclic potentiodynamic polarization (CPP), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The study was also complimented by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) investigation. Corrosion measurements indicated that the presence of Gr and the increase of its content raise the corrosion rate and reduce the polarization resistance of Al. Increasing the immersion time of the test samples in the chloride solutions before measurements was found to decrease the general corrosion and increase the pitting corrosion. SEM/EDX investigations revealed that the presence of Gr activates the corrosion of Al due to the occurrence of galvanic corrosion and this effect increases with increasing Gr content.