The Phase Relations Of The Zn–Fe–Ti Ternary System

Hot-dip galvanizing is an economical and effective method widely used for protecting steel and iron substrates from corrosion. Galvanizing Si-containing steels is a technical challenge because of the Sandlin effect which will result in bad quality of the coating. The addition of alloy elements can inhibite the Si reactivity, Ti is a candidate element. In addition, with the development of the auto industry, galvanizing high-strength steel has developed quickly. However, the effects of Ti in IF steel on Fe-Zn reaction remains to be further studied.The information of phase diagram is of great importance for material processing and alloy designing. The research on the phase equilibria of Zn-Fe-Ti-Si and Zn-Fe-Ti-Al quaternary system is helpful for understanding of the mechanism how Ti control the Si reactivity and the process of galvanizing IF steel, and designing appropriate dip alloy and technology. As the basis of system study, the phase equilibria of Zn-Fe-Ti ternary system has been experimentally determined in this paper.In present work, the isothermal sections of Zn-Fe-Ti ternary phase diagram at 600°C and 750°C are experimentally constructed by equilibrated alloys and diffuse couple, using scanning electron microscopy coupled with energy dispersive x-ray spectroscopy (SEM-EDS) and x-ray diffraction (XRD). The results show that: In these two isothermal sections, three Ti-Zn compounds named TiZn₃,TiZn and Ti₂Zn and a ternary T phase are found. In the isothermal section at 600°C, the T phase equilibriums with all the phases around it exceptα-Fe,Ti₂Zn,α-Ti andβ-Ti. There are seven three-phase regions were determined experimentally in the zinc-rich corner of the isothermal section, namely T+TiZn₃+η-Zn, T+TiZn+TiZn₃, T+δ+η-Zn, T+δ+Γ, T+TiZn+TiFe, T+TiFe₂+TiFe and T+TiFe₂+Γ. According to the Ti-Zn binary phase diagram put forward by Vassilev, the transition temperature of TiZn₇ is 609°C, but it was not found in the experiment. Thus, it is inferred that the transition temperature of TiZn₇ is lower than 600°C. The range of T phase composition is narrow, but the amount of iron and titanium, especially the iron conternt of T phase is higher than these at 450°C. The solubility of Ti inη-Zn phase is small, or almost zero, while it has a small amount of solubility inδphase andΓphase. Fe has a greater solubility in TiZn₃ and TiZn_, the largest solubility is separately the 3.8 at.% and 8.2 at.%. Zn has a certain solubility in TiFe and TiFe₂, and it's solubility in TiFe₂ is larger than TiFe. There are seven three-phase regions were determined experimentally in the zinc-rich corner of the isothermal section at 750°C, T+TiZn3+η-Zn , T+TiFe₂+η-Zn, T+TiZn3+TiFe, TiZn+TiFe+TiZn3, T+TiFe₂+TiFe and TiFe₂+Γ+α-Fe. Massalski's studies have shown that the transition temperature of TiZn3 is 650°C, but we still find TiZn3 at the experimental temperature 750°C. The solubility of Ti inη-Zn phase is small, or almost zero. Fe has a low solubility in TiZn3, while it still has a high solubility in TiZn. Zn has a large solubility both in TiFe and TiFe₂, especially in TiFe.