The Phase Relaitons Of The Zn-Al-Fe-Ti System

Hot-dip galvanizing is one of the most effective methods for improving the corrosionresistance of steel. Galvalume is one of the hot-dip galvanizing measurement, developedrapidly in recent years, which may substitute the pure znic of the hot-dip galvanizing.Due to the excessive thickness of its coating microstructure and the overabundancebottom dross problems, Galvalume's development is restricted unquestionably. For deeperunderstanding of the effect mechanism of adding Ti to the Zn-Al alloy, the 600℃isothermal section of Zn-Al-Ti ternary system and rich-Al corner of Zn-Al-Fe-Tiquaternary system with the Al being fixed at 75at.% have been investigated, and usingCALPHAD method calculates the phases relation of Zn-Al-Ti ternary system. As result ofthe existing questionably region of Zn-Ti binary system, this binary system has beenanalysed and optimized renewedly.In the optimization process of Zn-Ti binary system,there wasn't any other phasebetween TiZn₃ and TiZn₁₆,with the TiZn₇ and TiZn₈ considered as Ti₃Zn₂₂,the TiZn15considered as TiZn₁₆. The transition temperature of the Ti₃Zn₂₂ phase was approximately593℃in the optimization result, so Ti₃Zn₂₂ phase should not exist at 600℃(±5℃temperature error).The 600℃isothermal sections and the phase relations of Zn-Al-Ti ternary systemand Zn-Al-Fe-Ti quaternary system were determined by the equilibrated alloys approach,and the specimens were investigated by means of scanning electron microscopy (SEM)equipped with energy dispersive X–ray spectroscopy (EDS) and X–ray diffraction(XRD).Experimental results show that the 600℃isothermal section of the Zn-Al-Ti systemconsists of seven ternary phse regions:TiAl₃+T₁+α-Al,η-Zn+T₁+α-Al,η-Zn+T₁+TiZn₃,TiZn+T₁+TiZn₃,T₂+T₁+TiZn,T₂+T₁+Ti₃Al,TiAl₃+T₁+TiAl；T₁ is in equilibrium withall phase in the system, which has a relatively large composition range of znic andaluminum while tiumium remains nearly between 22.85～30at.%. While T₂ is only inequilibrium with T₁, Ti₃Al and TiZn. Based on the experimental results of this work andrelated data of the binary system, the Zn-Al-Ti ternary system was extrapolated byCALPHAD technique. The result fixed well with the experiment .In the Zn-Al-Fe-Ti quaternary system at 600℃was found exist 2 four-phase regions[T₁+TiAl₃+FeAl₃+α-Al and T₁+η-Zn+FeAl₃+α-Al], 5 three–phase regions [T₁+η-Zn+α-Al, T₁+TiAl₃+α-Al, T₁+FeAl₃+α-Al,η-Zn+FeAl₃+α-Al, TiAl₃+FeAl₃+α-Al] and 3 two–phaseregions[T₁+α-Al, FeAl₃+α-Al, FeAl₃+TiAl₃]. T₁ can coexist with all phases in thisisothermal section, respectively, no new quaternary phase was found in this study.This job had analysed T₁ phase crystal structure by Rietveld method, which is fccPm 3 m(L₁₂)structure, Zn atom position replaced by Al atom and Zn/Al occupied(0,0.5,0.5) position.