Role of Alloying Additions on the Dissolution Kinetics of Aluminum Binary Alloys Using Artificial Crevice Electrodes

Dissolution kinetics of binary Al alloys containing Cu, Zn, and Mg in chloride solution were investigated using the artificial crevice technique. The alloys were potentiostatically held at 0 V vs saturated calomel electrode (SCE) to pass a certain charge density, and the potential was then scanned down to obtain the artificial crevice polarization curve. The addition of alloying elements alters the repassivation potential by altering the dissolution kinetics. The addition of Cu raises the repassivation potential and lowers the dissolution kinetics. Zn addition decreases the repassivation potential and enhances the dissolution kinetics. Mg additions have little or no effect on the repassivation potential and the dissolution kinetics. Dissolution kinetics in the crevice were influenced by both the ohmic drop and surface overpotential. Voltage component calculations indicate that the main role of the alloying elements is to alter the surface overpotential for metal dissolution and thereby shift the position of the polarization curves on the potential axis.