The Phase Relations Of The Zn-V-Sb Ternary System

The hot-dip galvanizing process is known as one of the techniques frequently used for enhancing the corrosion resistance of steel. Adding alloy elements into the zinc bath affects the structure and the surface quality of the coating. For traditional batch galvanizing, vanadium（V） can be an effective additive to molten Zn for controlling the Si reactivity of steels with high Si contents. In the primitive galvanizing technology, lead was frequently added to the zinc bath to improve the fluidity of molten zinc and the development of spangles at the coating surface. However, galvanizing with Pb-containing alloys（technically very suitable, but hazardous for the environment and health） has been recently restricted. The replacement of the alloys became a very important task. It should be mentioned that antimony（Sb） is a more effective additive in a zinc bath than Pb, because it not only has a function similar to Pb in a zinc bath, but also makes the crystal particles smaller and reduce zincilate. To get a better understanding of the effect of V and Sb on galvanizing, deeply investigation on the Fe-Zn-V-Sb quaternary phase diagram and its thermodynamic relations should be done to guide hot-dip galvanizing. At present, only the Zn-V-Sb ternary alloy phase diagram has not been reported yet, so it’s important to research the Zn-V-Sb ternary system.Phase relations in the Zn-V-Sb ternary system have been studied experimentally for the whole composition range for three temperatures, 450, 600 and 800 °C, using scanning electron microscopy coupled with energy-dispersive spectrometry and X-ray diffraction. The ternary compound VZn Sb, mentioned in the literature, exists at 450 and 600 °C, but disappears at 800 °C. And the ternary compound could be equilibrated with Liq., Sb₃Zn₄, V₃ Sb, Sb Zn and Sb₂Zn₃. Twelve different tri-phase regions could be confirmed in this system at 450 °C, i.e., α-Sb + VSb₂ + Sb Zn, VSb₂ + VSb + Sb Zn, VSb + V₃ Sb + Sb Zn, V₃ Sb + VZn Sb + Sb Zn, Sb₃Zn₄ + VZn Sb + Sb Zn, Liq. + Sb₂Zn₃ + VZn Sb, Liq. + V₃ Sb + VZn Sb, Liq. + V₃ Sb + VZn₃, V₃ Sb + VZn₃ + α-V, V₃Sb₂ + VSb + V₃ Sb, Sb₃Zn₄ + Sb₂Zn₃ + VZn Sb and V₄Zn₅ + VZn₃ + α-V. Moreover, the experimental results indicate that eight tri-phase regions could be confirmed in the system at 600 °C, i.e., Liq. + α-Sb + VSb₂, Liq. + V₃Sb₂ + VSb₂, Liq. + VZn Sb + V₃Sb₂, Liq. + VZn Sb + V₃ Sb, Liq. + V₃ Sb + VZn₃ and V₄Zn₅ + V₃ Sb + α-V. Four tri-phase regions exist in the 800 °C isothermal section, i.e., Liq. + VSb₂ + V₅Sb₄, Liq. + V₃Sb₂ + V₅Sb₄, Liq. + V₃ Sb + V₃Sb₂ and Liq. + V₃ Sb + α-V. On the other hand, the maximum solubility of Zn in V₃ Sb and V₃Sb₂ decreased with the increase of the temperature; The solubility of Sb in VZn₃ and V₄Zn₅ is very limited; Meanwhile, the solubility of V in Sb₂Zn₃、Sb₃Zn₄ and Sb Zn is very limited.