Study on the behavior of additives in steel hot-dip galvanizing by DFT calculations

Two types of additives in hot-dip galvanizing, effective additives Ni, V, and Ti used industrially to reduce the coating thickness of zinc-iron, and noneffective additives Mg, Sn, and Ag showing quite different behavior from the former, were studied with density functional theory calculations by using cluster models. The optimized geometric configurations, total energy, electronic density of states, and electronic charge distributions for the additive-zinc associates were obtained. Results indicated (1) the effective additives have much stronger bonding energy with zinc than the noneffective additives, (2) the electronic charges significantly shift from the zinc atoms to the Ni, V, or Ti atoms, while only a little shift to the Mg, Ag, or Sn atoms occurs, and (3) the Fermi energy level and the band gap of zinc clusters obviously change, owing to adding Ni, V, or Ti, but these effects do not occur for the second type of additives. On the basis of the calculated results, the underlying mechanism of additive effect on the formation of Fe-Zn intermetallics (and/or coating thickness) was proposed.