Effect of strip entry temperature on the interfacial layer and corrosion behavior of galvanized steel

Abstract

The present work investigates the effect of three different strip entry temperatures (SETs) (500, 575, and 650 ?) on the extremely thin aluminum (Al)-rich inhibition layer formed at the substrate-coating interface during galvanization in a Zn-0.2 wt% Al bath and its correlation with the corrosion behavior in freely aerated 3.5 wt% NaCl solution. The scanning electron microscopy confirms that the morphology of the interfacial layer becomes coarser with an increase in SET. Moreover, the rate of Al uptake at the interfacial layer increases with increasing the SET due to an increase in the effective reaction temperature for the nucleation of Fe-Al crystals at the substrate liquid zinc interface. X-ray diffraction also reveals that the texture coefficient (TC) of the preferred high atomically dense (0002) basal plane of Zn coating is pronounced at lower SETs. It has been found that the coating prepared at 500 degrees C has the lowest corrosion rate of 0.142 mm/y as compared to that prepared at 575 degrees C (0.245 mm/y) and 650 degrees C (0.266 mm/y). Electrochemical impedance spectroscopy also follows a similar trend. It has been observed that the dominance of the highest packing density (0002) crystal plane, compact interfacial layer as well as uniform and compact pore-free coating surface have resulted in the lowest corrosion rate of the coating made at the lowest SET of 500 degrees C.