Effect Of Co And Ti On The Coating's Microstructure And Correlated Phase Equilibria

Hot dip galvanized steels is are widely used in various fields for the excellent corrosion resistance property.Si elements are usually inevitably added to steel as deoxidizers or strengthening elements.However,Si reactivity still is a technical challenge for hot-dip galvanized steels,which make the excessive plating and poor adhesion of the coating to the substrate,it seriously hinders the development of hot dip galvanizing.The addition of alloying elements to the zinc bath can effectively inhibit silicon reactivity.The addition of 0.02 wt.%Ti to the zinc bath serves to inhibit the reactivity of the Q235 steel.When 0.075 wt.%Co was added to the zinc bath,the silicon reactivity of the Q235 steel was completely suppressed.In this work,This work focused on the phase relationship of Co-Ti-Zn ternary system and the effect of Co and Ti synergy on the microstructure of galvanized layer..The research results enrich the zinc-based alloy database and develop a new type of Zn-Co-M galvanized alloy has a certain guiding role.In this work,the equilibrium alloy method was adopted to determine the phase relation of the Co-Ti-Zn ternary system.The specimens were investigated by means of optical microscopy,scanning electron microscopy-energy spectrometer analysis and X-ray diffraction.The results show that eleven three-phase zones are determined in the isothermal section at 450?,i.e,L-Zn+?₂+?₁,L-Zn+?₁+TiZn₁₆,?₁+Ti₃Zn₂₂+TiZn₁₆,?₁+Ti₃Zn₂₂+TiZn₃,CoTi+?₁+TiZn₃,CoTi+?₁+?,CoTi+?₁+?,Co₃Ti+?₁+Co₂Ti,CoTi+TiZn₃+TiZn,CoTi+TiZn+Ti₂Zn,CoTi+Ti₂Zn+CoTi₂.Eight three-phase zones were determined in the isothermal section at 600?,i.e,L-Zn+?₁+Ti₃Zn₂₂,?₁+Ti₃Zn₂₂+TiZn₃,CoTi+?₁+TiZn₃,CoTi+?₁+?,CoTi+?₁+?,CoTi+TiZn₃+TiZn,CoTi+Ti₂Zn+TiZn,CoTi+Ti₂Zn+CoTi₂.Co is almost insoluble in Ti-Zn intermetallic compounds,and the solubility of Ti in?₂,?₁,?,and?₁is 0.1 at.%,5.2 at.%,2.1 at.%and 2.1 at.%,respectively.No ternary compounds were found in either of the two sections.The hot-dip galvanizing method was carried out by drying solvent method.The effects of synergistic effect of Co and Ti on the microstructure of Q235 steel coating were studied.The microstructure of the coating and the chemical composition of each phase were analyzed by scanning electron microscopy-energy spectrometer.Studies have shown that the addition of Co and Ti elements to the zinc bath can obtain a denser coating structure,the thickness of the intermetallic compound is reduced,the silicon reactivity is well suppressed,and the interfacial reaction of the coating is controlled by diffusion.When 0.03 wt.%Co and 0.02 wt.%Ti were added to the zinc bath,the growth rate time index is 0.42.When 0.04 wt%Ti and 0.05 wt%Co were added to the zinc bath,the growth rate time index of the coating layer was 0.17,the?phase was the thinnest,and the?phase did not change significantly.The silicon reactivity of Q235 steel was completely suppressed.