Editors' Choice—Dealloying of MgZn2 Intermetallic in Slightly Alkaline Chloride Electrolyte and Its Significance in Corrosion Resistance

Abstract

The role of dealloying in the corrosion resistance of MgZn2 has been investigated for the first time. The elemental dissolution kinetics of a synthetic, nominally pure MgZn2 intermetallic compound was investigated and compared with pure Mg and Zn in 30 mM NaCl with pH = 10.1. Atomic emission spectroelectrochemistry was used to monitor Zn and Mg dissolution as a function of time at open circuit, during linear scan polarization, and at various applied potentials. Zn and Mg displayed a mutual inhibitive effect at open circuit which was explained by the formation of Mg depleted Zn / Zn oxide film. Polarization experiments revealed a Type II dealloying mechanism in which Zn and Mg dissolve simultaneously and congruently above the critical potential, Ec, while preferential Mg dissolution dominates below Ec. Preferential Mg dissolution leads to the formation of a Mg depleted metallic Zn layer which suppresses further Mg dissolution. In oxygen saturated electrolyte, O2 reduction was the major cathodic reaction on Zn but was completely inhibited on Mg. The intense cathodic reduction of O2 on Zn led to a cathodic dissolution of Zn, probably due to the increased interfacial pH.