Study on Initial Corrosion Behavior of Arc-thermally Spray Zn, Zn–Al, and Al–Mg Coatings Exposed in Atmospheric Environment for One-Year

This paper presents the results of a study comparing the initial corrosion characteristics of thermal spray coatings on Zn, Zn-Al, and Al–Mg thermal spray coatings after one year atmospheric exposure tests at two atmospheric environment sites. The thermal spray coatings were obtained by electroric arc spraying of various metals onto a carbon steel substrate. Atmospheric exposure tests were also conducted for outdoor accelerated exposure tests in which test specimens were applied with artificial seawater. The corrosion properties of these spray coatings were evaluated by surface analysis, film thickness measurements, cross-sectional analysis and anodic/cathodic polarization measurement. After one year of atmospheric exposure testing, white, granular corrosion products were observed on the surface of the Zn and Zn-Al thermal spray coatings, while no significant changes were observed in the Al–Mg thermal spray coating. Similar results were obtained for the surfaces of test specimens in atmospheric exposure tests with artificial seawater. The thickness of the thermal spray coating increased for the Zn thermal spray coating, while no significant change was observed for the other thermal spray coatings. Thus, differences in corrosion behavior were observed due to the composition of the thermal spray coatings. The initial corrosion behavior of the thermal spray coatings was also investigated based on the results of coating morphology and cross-sectional elemental distribution of the coatings.