Anodic Corrosion of Zinc Alloys in Seawater

Abstract

Zinc alloys are widely used as sacrificial anodes in cathodic protection systems. In order to better understand the corrosion performance of these alloys the structure and morphology of corrosion products have been studied under laboratory conditions as a function of time, potential, current density, temperature, and velocity. Polarization curves have been determined and scanning electron microscopy, energy‐dispersive x‐ray microanalysis, and x‐ray diffraction have been utilized to identify and characterize surface corrosion. Nucleation and growth processes for the primary anodic electrocrystallization product, , have been determined. A dissolution‐precipitation mechanism is postulated, which describes the development of network arrays of zinc oxide platelets. The relationship of anodic corrosion to microstructural features of the bulk alloy is also described, including the role of grain boundaries and second‐phase particles. Conditions leading to formation of passivating thick films are discussed.