Segregation of alloying elements during the hot-dip coating solidificationprocess

Hot-dip galvanized steel is the most frequently used among coated steels. H ot dip coatings are characterized by their appearance. Visually, they show shiny and dull grains with different morphologies. The solidification morph ology and the alloying elements segregation affect the final properties of the coating. In this paper, the surface segregation of aluminium and antimony was studie d in relation to the coating topography, which is the result of the orienta tion of the solidification structure with respect to the sheet. Two morphol ogies can be observed on the galvanized material: one of a feather type app earance and another with a granular appearance. Solidification structures c orresponding to these surface morphologies were characterized: in the feath er type the dentrites grow parallel to the substrate surface, and in the gr anular one they grow forming an angle. Microsegregation in the grains with the dendritic solidification of zinc wa s detected, A surface enrichment of aluminium and antimony was also observe d on areas with dendritic growth running at an angle to the substrate surfa ce. This segregation helps to explain the 'surface darkening' defect which is observed in aged galvanized materials, (C) 1999 Elsevier Science S.A. Al l rights reserved.