The role of texture and microstructure in optimizing the corrosion behaviour of zinc hot-dip coated steel sheets

Abstract

Protective metallic coatings based on Zn are usually used to protect steel against corrosion. When coated steel sheets are subjected to corrosive environments, its corrosion behaviour is affected due not only to changes of the coating texture, but also of the microstructure. The aim of this work was to study the effects of texture components and microstructure on the corrosion behaviour of hot-dip galvanized coatings. Texture components of the coatings were evaluated employing X-ray diffraction whilst its corrosion resistance was analyzed by means of Tafel polarization and salt spray tests. Microstructure of the coatings was studied using SEM and EDS analysis. From the experimental results, it was concluded that increasing the lead content of the zinc bath would decrease the texture coefficient of basal plane component and conversely, the texture coefficient of other components such as high angle pyramids, low angle pyramids and prism planes would be increased. Besides, gamma layer thickness increases as the lead content of the zinc bath increases. In addition, it was observed that greater basal texture coefficient and smaller gamma layer thickness would result in better corrosion resistance of hot-dip galvanized coatings. © 2008 ISIJ.