Effect of Light Illumination on the Corrosion Behavior of Mg-RE Alloy EV31A in Chloride-Alkaline Solutions

Abstract

The effect of white light illumination on the corrosion behavior of a Mg - Rare Earth (RE) alloy EV31A specimens in peak aged condition was investigated in 0.1 M NaOH solution containing 0, 80, 100 and 200 ppm chloride ions at room temperature. The passivation current density decreased upon illumination in the 0.1 NaOH solution without chloride addition. On the other hand, increased passive current densities were observed in the chloride containing solutions upon illumination. The white light illumination did not affect the open circuit potential of the EV31A. This result indicated that alloying additions did not significantly alter the bandgap of the passive layer or induce bandgap states in the passive layer in order to harvest the longer wave lengths of the white light. The incubation time for passivity perturbation decreased with illumination. The charge carrier density increased significantly upon illumination. The exchange current density for hydrogen evolution increased under the illuminated conditions. The Mott-Schottky results pointed out that light illumination induced surface defects of n-type character. These defects could have been potential sites for chloride adsorption that decreased the stability of the passive film. The white light illumination did not result in induced photo potential due to wide bandgap of the passive layer. Since the band bending was not altered, the electric field remained the same in both illuminated and non-illuminated condition. Overall, illumination of white light did not offer significant benefit to the localized corrosion resistance of the Mg-RE alloy in alkaline-chloride solutions.