The aim of this study was to clarify the effect of the silicon content in steel on the structure of hot-dip galvanized zinc coating. It was found that in steel samples containing the silicon in an amount of about 0.1% and 0.5% the increased thickness coating was formed. This fact was associated with structural features of the ζ-phase. Energy dispersive microanalysis had shown the maximum concentration of silicon in the coating was observed in ζ-phase on St3 steel (Si = 0.1%) and in the fine mixture of 5 and ζ-phase on 09G2S steel (Si>0.5%). This phenomenon was analyzed using a Zn-Fe-Si system diagram and its polytermic sections. It was found that there were eutectic reactions of decomposition the liquid to mixture (ζ+η+ FeSi) phases at the content of silicon in steel about 0.1% and more than 0.5%. Particles of FeSi-phase were involved in the dissolution of Γ and δ phases, which led to a direct contact of the melt and the steel substrate. This process was accompanied by the intensive ζ-phase formation and the rapid growth of coating thickness.
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