The Influence Of Vanadium On The Galvanized Coating And Phase Relations Of The Zn-Fe-Al-V Quaternary System

The corrosion of steels has been a main failure form in modern industry and ithas caused heavy losses to national economy. Hot-dip galvanizing is a relativelyeconomical anti-corrosion technology, and its further research and development willafford a substantial base to our economic development. As a significant rare element,vanadium has been researched for the recent decades. Therefore, studying the effectof the vanadium to hot-dip galvanizing has significant impact to develop zinc basealloy which is anti-corrosion and environment friendly.Aluminum is a common adding element in hot-dip galvanizing. With the additionof the Al, an inhibition layer Fe₂Al₅is formed to prevent the growth of the alloy layer.Zinc-aluminum and zinc-aluminum alloys which have good corrosion resistance andhigh-temperature oxidation resistance are important zinc alloys, such as Galfan,Galvalume and so on. In the present work, the Zn-Fe-Al-V quaternary system hasbeen researched experimentally. The results of this research are benefit forunderstanding the synergistic effect of Al and V to hot-dip galvanizing.Based on the information of the Zn-Fe-Al, Zn-Fe-V, Zn-Al-V ternary systems,the450°C isothermal sections of the Zn-Fe-Al-V quaternary system with zinc fixed at93at.%has been determined experimentally by means of optical microscopy,scanning electron microscopy coupled with energy-dispersive spectrometric andX-ray diffraction. Results indicate that there are six four-phase regions, i.e., L+T （V）+ζ+VZn₃, L+VZn₃+ζ+δ，L+VZn₃+T （Al）+δ，L+T（Al）+VZn₃+Al₃V，L+T（Al）+Fe₂Al₅+Al₃V，L+Fe₂Al₅+FeAl₃+Al₃V have been identified in the presentwork. The maximum solubility of the Fe in Al₃V is1.8at.%, and the maximumsolubility of the Al in VZn₃is24.4at.%. The maximum solubility of Zn in Fe₂Al₅,FeAl₃and Al₃V is14.4at.%,6.1at.%and12.0at.%, respectively. The T（Al） phase ofthe Zn-Fe-Al ternary system and the T（V） phase of the Zn-Fe-V phase both exist inthe Zn-Fe-Al-V quaternary. The solubility of V in T（Al） is4.7at.%, and the maximumsolubility of the Al in T（V） phase is0.2at.%which is relatively small. There is nonew quaternary phase found in the work.The effect of the vanadium to hot-dip galvanizing has been researched from theV-containing steels and zinc bath with vanadium addition by using drying solventmethod with SEM-EDS analyses. Results show that the vanadium element can promote the formation of Γ phase either in the V-containing steels or zinc bath withvanadium. The galvanizing coatings of V-containing steels consist of ζ, δ and Γ. Thegalvanizing organization of the pure steels galvanize in zinc bath with vanadiumcontains three layers, i.e., T（V）, δ and Γ. The addition of V to zinc bath has changedthe diffusion path which leads to the formation of the T（V） layer instead of the ζ layer.With the adding of V to the steel, the nucleation rate has been decreased but the cracksof the δ layer have been increased.