Effect of alloying element segregation on the work of adhesion of metallic coating on metallic substrate: Application to zinc coatings on steel substrates

A thermodynamic model based on the ‘Macroscopic Atom’ approach is proposed to assess the effect of alloying element segregation on the adhesion of metallic coating on metallic substrate. The interfaces that occur in hot-dip galvanized steels are considered, which include: Zn/Fe, Zn/Fe2Al5, Zn/FeZn13, FeZn13/Fe2Al5, and Fe2Al5/Fe. The effect of the alloying element on the work of adhesion of these interfaces is investigated, which includes Mg, Al, Si, P, Ti, V, Cr, Mn, Fe, Ni, Zn, Nb, Mo, Sn and Bi. Among these elements, Bi, Sn and Mg are predicted to decrease the work of adhesion of the Zn/Fe interface, whereas P, Nb, Mo, V, Ti and Ni tend to enhance this adhesion. The effect of element M (M = Al, Si, Cr, Mn) is positive when it exists in the zinc coating or negative when it occurs in the iron substrate. Among these interfaces, the Fe2Al5/Fe interface with a value of 3.8 J m−2 is the strongest, whereas the Zn/FeZn13 interface with of a value of 1.7 J m−2 is the weakest. Delamination of the coating upon deformation is predicted to occur along the FeZn13/Fe2Al5 and Zn/Fe2Al5 interfaces. This agrees with microscopic observations of hot dip galvanized steel after tensile testing.