Electrochemical corrosion studies on coated sheet steel

Abstract

The corrosion of zinc- and zinc- alloy coated steels was measured by electrochemical methods in 0.1 N and 1.0 N sodium chloride solution. The purpose was to develop improved testing methods for quality control and development of improved coatings. In order to study the effect of galvanic coupIing between coating and substrate steel, a scribe was machined in the coating to expose the steel which, in turn, was exposed to electrolyte. The purpose was to simulate service conditions wherein coating may be mechanically damaged. It was found that corrosion rate of coating, regardless of composition, increased in deaerated solutions. In solutions containing dissolved oxygen this was not always the case because of the non - reproducibility of migration of dissolved oxygen to corroding surface. Although it was difficult to distinguish between pure zinc coatings, demarcation between pure zinc- and alloy- coatings was possible.