Study On The Effect Of Ce On Hot-dip Aluminized-zinc Coating And Its Correlate Phase Equilibrium

23 wt.% Al-Zn(i.e.,42 at.% Al)coating is of interest to galvanized workers due to their excellent integrated performance.However,in the actual production,there are brittle intermetallic compounds,which are likely to form cracks,and the coating is too thick.These problems limit its wide range of applications in the industry.Rare earth elements have the functions of purification,degassing,removing impurity,refining grain,strengthening matrix and improving performance.The addition of rare earth Ce to the 23 wt.% Al-Zn bath can improve the quality of the coating.This research is mainly aimed at investigate the effect of Ce on hot-dip Aluminized-Zinc coating and its correlate phase equilibrium.The research results are of great significance and have application value to enrich the aluminum-zinc alloy database and to develop new rare earth added aluminum-zinc alloy.The phase relationships in the Al-Zn-Ce,Al-Fe-Ce ternary systems and the Al-Zn-Ce-Fe quaternary system at 540 °C with 42 at.% Al were measured by means of scanning electron microscopy(SEM)and energy dispersive spectroscopy(SEM),X-ray diffraction(XRD).The experimental results show that there were 4 three-phase regions and 1 ternary compound τ2 in the isothermal section of Al-Zn-Ce(42~100 at.%Al)ternary system at 540 °C.In Al-Fe-Ce(0~66 at.%Al)ternary system,the experiment obtained 10 three-phase regions and the 2 three-phase regions were deduced.3 ternary compounds Ψ1,Ψ2,Ψ3 were determined in this isothermal section.The composition and the X diffraction pattern of Ψ3 were preliminary defined in this work.3)The phase relations of the Al-Zn-Ce-Fe quaternary system at 540 °C with 42 at.% Al were measured,the experiment obtained 10 four-phase region,i.e.,τ2+ɑ-Al+FeAl3+Liq.,Ψ1+τ2+FeAl3+Liq,FeAl3+ Fe17Ce2+τ2+CeZn2,FeAl3+Al2Ce+τ2+CeZn2,Al2Ce+Ψ1+Fe17Ce2+τ2,FeAl3+Fe2Al5 +Liq+Ψ1,FeAl3+Ψ1+Fe17Ce2+τ2,FeAl+Fe2Al5+Ψ1+Liq.,Ce2Zn17+FeAl3+ɑ-Al+Liq.,and 8 three-phase regions.No four compound was found,an Al-Zn-Ce ternary compound τ2 and an Al-Fe-Ce ternary compound Ψ1 were existed in the system.The effects of Ce and immersion time on the apparent quality,microstructure and growth kinetics of aluminum-zinc coating were studied by means of scanning electron microscopy and energy dispersive spectroscopy.The results show that adding a certain amount of Ce element in the molten pool can reduce the zinc tumor,improve the brightness and flatness of the surface of the coating,and improve the apparent quality of the coating.The growth of Fe-Al alloy layer required a certain incubation period,and the addition of Ce can shorten the incubation period.The growth of Fe-Al alloy layer was controlled by interfacial reaction when Q235 steel was dipped in 23 wt.%Al-Zn bath.When the Ce was added into the aluminum-zinc pool,the growth rate index of the alloy layer was lower than that of the Ce-free coating.The growth trend of the alloy layer was controlled by the interface reaction and the diffusion reaction.