The Phase Relations Of Zn-Fe-Ni-Sb Quaternary System And The Effect Of Ni And Sb On The Microstructure Of Galvanized Coating

Hot-dip galvanizing is a cheap and effective method in steel anti-corrosion technology. Because of its simple production technology and low production costs of hot dip galvanized products, hot-dip galvanizing widely used in the electricity, ship and automotive industries. However, there exists a technical problem in hot-dip galvanizing containing silicon, namely silicon reactivity. The silicon reactivity that caused by silicon brings the growth of the coating too thick, coating the performance becomes poor during containing silicon steel in the process of hot-dip galvanizing. At present, the most common solution of the silicon reactivity is to add different alloy elements into the pool of zinc to inhibit the plating overgrowth. To add a certain amount of Ni element in zinc bath not only controls the silicon reactivity of Sandelin steels well, but also increases the liquidity of the zinc bath. Studies have shown that adding a small amount of Sb to zinc bath can reduce the zinc slag, refine grains and enhance mobility, and also form a beautiful flower in the coating. In the present work, the effect of both additions Ni and Sb on Si-containing steels galvanized coating and the phase relationships of the Zn-Fe-Ni-Sb quaternary system have been investigated.This experiment adopts the method of study is balanced alloy method, combining with the methods of the scanning electron microscopy and energy dispersive spectroscopy(SEM-EDS) and X-ray power diffraction(XRD) to determine the phase relations in the Zn-rich corner of the 450℃ isothermal section of the Zn-Fe-Ni and Zn-Fe-Ni-Sb systems and the 600℃ isothermal section of Zn-Fe-Ni-Sb systems with Zn being fixed at 93 at.%. Two three-phase regions, i.e., L + T + δ, T+L+ γ are found in the Zn-rich corner of Zn-Fe-Ni system. The Zn-rich corner of the 450℃ isothermal section of the Zn-Fe-Ni-Sb quaternary system contains 3 four-phase regions, i.e., L + ζ + T + Sb2Zn3, L + T + γ + Sb2Zn3 and L + T + γ + δ-NiZn, and 7 three-phase regions, i.e., L + ζ + Sb2Zn3, L + ζ + T, L + T + Sb2Zn3, L + γ + Sb2Zn3, L + T + γ, L + T + δ-NiZn and L + γ + δ-Ni Zn. The Sb solubility in the ζ-FeZn phase is very limited, and it almost insoluble in the δ-Ni Zn phase. However, the maximum solubility of Sb in the γ-NiZn phase is 1.9 at.%. The solubilities of Fe and Ni in the Sb2Zn3 phase are 0.6 and 0.9 at.%, respectively. In addition, no new phase was found in the study. There are 2 three-phase regions, i.e., L + T + δFe and L + T + γ, but no four-phase regions in the Zn-rich corner of the 600 ℃ isothermal section of the Zn-Fe-Ni-Sb quaternary system.In this work, the effect of both additions Ni and Sb on the silicon content is 0.202 wt.% of Q235 steel hot-dip galvanizing coating has been investigated. Contrastive analysis the effect of hot-dip galvanizing time and different content of Ni and Sb in the zinc bath on hot-dip galvanizing coating organization and thickness. The results show that: only add Sb in the zinc bath can’t reduce the hot-dip galvanizing coating thickness of Q235. Add both Ni and Sb in zinc bath can suppressing Fe-Zn interface reaction, so as to reduce the thickness of the hot-dip galvanizing coating. To the Q235 steel that contains 0.202 wt.% silicon, add 0.05 wt.%Sb and 0.4 wt.%Ni into the zinc bath could achieve perfect coating.