Study of aluminium inhibition layer formed during hot dip stage of galvannealing on titanium interstitial free and rephosphorised titanium interstitial free substrates

Abstract

A study has been made of the Al inhibition layer that forms on interstitial free (IF) steel substrates on immersion into a Zn spelter typical of that used in commercial galvannealing. Techniques used to study the layers formed included SEM, Strata, and SNMS. A relatively featureless, continuous layer formed after 0·15 s immersion. The layers consisted of an Fe–Al intermetallic phase containing Zn in solution. Results suggest that the layer formed on rephosphorised Ti IF substrates is thicker than that formed on Ti IF substrates containing lower P levels. This may contribute to the alloying problems that can be encountered during the commercial galvannealing of increased P steel grades. Quantitative depth profiles through the layers have allowed examination of layer composition and thickness and enabled a study of inhibition layer/ substrate interface chemistry, providing evidence of the association of Mn, P, and O with the layers.