Effect of coating thickness on modifying the texture and corrosion performance of hot-dip galvanized coatings

Abstract Hot-dip galvanized zinc coating is the most frequently used among coatings to protect steel against corrosion. When coated steel sheets are subjected to a corrosive environment, its corrosion behaviour is affected by texture and microstructure variations. The aim of this research work was to study the texture and corrosion resistance of hot-dip galvanized zinc coatings affected by the coating thickness and chemical composition of the zinc bath. Texture of the coatings was evaluated employing X-ray diffraction whilst its corrosion behaviour was analyzed using Tafel polarization test. Experimental results showed that (00.2) basal texture component would be weakened by increasing the lead content of the zinc bath and coatings with strong (00.2) texture component have lower corrosion current density than the coatings with weak (00.2) texture component. Furthermore, it was inferred that by increasing the thickness of the coatings with the same content of lead in the zinc bath, the relative intensity of (00.2) texture component and corrosion resistance of the coatings would be decreased and conversely, relative intensity of (20.1) high angle pyramidal planes and (10.0) prism planes would be increased due to establish a balance between surface and strain energies. Besides, five types of morphology were observed on the surface of hot-dip galvanized coatings in dull and bright spangles. Finally, it was recognized that the main corrosion product of the salt spray test is Simonkolleite.