Effect of Elevated Strip Entry Temperature on the Aluminum Rich Inhibition Layer at the Substrate Coating Interface During Galvanizing

Abstract

During continuous hot dip galvanizing, the use of higher line speeds and thicker gauge strip often results in the steel strip entering the bath at a temperature significantly higher than that of the zinc bath. Studies on the effect of elevated strip entry temperature on the galvanizing reactions are limited. This investigation evaluates the microstructures of galvanized steel produced in a zinc bath containing 0.2 wt% dissolved aluminum essentially to study the effect of elevated strip entry temperatures on the formation of an aluminum rich inhibition layer at the substrate-coating interface. It is concluded that the inhibition layer consists of the orthorhombic Fe2Al5Znx (0<x<1) phase and the morphology of the interfacial layer progresses from a fine crystalline to coarse grain structure with increasing strip entry temperature. Higher strip entry temperature facilitates the formation of zeta (zeta) phase in the coatings. It is also observed that the overall inhibition layer thickness increases with increasing strip entry temperature.