Study of growth mechanism of zinc hot dip galvanising coatings

Zinc hot dip galvanising is one of the most effective methods for the corrosion protection of ferrous materials. However, although its efficiency is undisputable, the exact growth mechanism of these coatings is still under question. In the present work, the diffusivity of liquid zinc in carbon steels was measured with electron microscopy. Furthermore, the change of the free Gibbs energy was calculated for each phase of the coating. Nevertheless, the coating structure was microscopically studied for an extremely short immersion time (about 1 s). In this way, it was deduced that the coating growth begins with the nucleation of the ζ phase of the Fe–Zn system. The γ and λ phases grow with zinc diffusion through the ζ phase. The η phase is mechanically drifted due to the surface tension of the liquid metal.