Formation Behavior of Alloy Layer in Initial Stages of Galvanizing

Abstract

The formation behavior of the alloy layer in the initial stages of galvanizing at 450°C has been investigated, using ultra low carbon Ti added steel sheet. The formation of Fe-Zn intermetallic compounds on the steel surface was retarded with the increase of Al content in galvanizing bath. For high Al content in the bath, Fe₂Al₅ intermetallic compound grew with dipping time. At the same time, diffusion of Zn into Fe₂Al₅ layer occurred. And furthermore, the outburst phenomenon was observed with the increase of immersion. The occurrence site of outburst structure corresponded well to grain boundary of the base steel. Fe₂Al₅ layer formed in the first step of immersion was fractured by the occurrence of outburst and dispersed in zinc coating. The formation mechanism of the outburst structure which means the initiation of growth of Fe-Zn intermetallic compounds was discussed.