Effect of indium on the microstructure and corrosion resistance of the galvanising coating.

This article investigates the effect of indium (In) addition to zinc baths on the microstructure and corrosion resistance of hot-dip galvanised coatings on Q235 steel, which contains silicon (Si). The study finds that indium promotes the formation of a dense Γ phase and allows up to 0.79 wt-% Si to dissolve in the ζ phase, reducing silicon segregation and inhibiting rapid ζ phase growth. Indium also decreases the diffusion coefficient of iron (Fe) atoms in the ζ phase, shifting the compound layer growth mechanism from interface reaction control to diffusion control. Electrochemical tests demonstrate that a Zn-0.4 at.-% In coating exhibits significantly improved corrosion resistance compared to pure zinc coatings, with lower self-corrosion current density and reduced corrosion area. These findings suggest that indium addition effectively suppresses silicon reactivity during galvanising and enhances coating durability on Si-containing steels.