| Hot-dip galvanizing is an effective and widely used technology to protect steelagainst corrosion. However, the hot-dip products are made more demands with theindustrial development, such as superior corrosion resistance. The Al-Zn alloy coatingexhibiting excellent performance becomes one of hot topics of the hot-dip, in which55wt.%Al-Zn coating develops rapidly because of comprehensive characteristics, butthere are some problems which are excessive thickness of coating causing poorformability and overmuch dross at continuous hot-dip process increasing cost. Theaddition of Bi, Si, RE et al. alloy elements to zinc bath in hot-dip galvanizing is acommon method by changing the type and forming order of the intermetalliccompounds to improve coating quality or change the type of the dross. The focus inthe work is the effect of Bi on the morphology and the dross in55wt.%Al-Zn bath,which is related to the reaction between Al, Zn, Bi and Fe. In the present work, therelated phase equilibria of the Al-Zn-Fe-Bi quaternary system is determinedexperimentally to provide theoretical basis for a better understanding the reactionbetween Fe and55wt.%Al-Zn bath containing Bi.Phase equilibria of the Zn-Fe-Bi, Al-Zn-Bi, fixed75at.%Al and50at.%Znsections in the Al-Zn-Fe-Bi isothermal tetrahedron at600℃were determined byequilibrated alloys method combined scanning electron microscopy (SEM) coupledwith energy dispersive X-ray spectroscopy (EDS) and X-ray powder diffraction(XRD). The following result are obtained, i.e.,(1) The L phase is in equilibrium withδ, Γ and α-Fe phase in the Zn-Fe-Bi ternary system at600℃, respectively.Twothree-phase regions L+α-Fe+Γ and L+Γ+δ have been identified, and no newternary phase is found. Bi is almost insoluble in δ, Γ and α-Fe, and the solubility of Fein the liquid phase is limited because of the existence of Bi in liquid phase.(2) Onethree-phase region L1+L2+(Al) has been confirmed in Al-Zn-Bi ternary system at600℃, and the liquid miscibility gap region is large.(3) One four-phase region L1+L2+FeAl3+(Al) has been identified in fixed75at.%Al section of the Al-Zn-Fe-Biisothermal tetrahedron at600℃.(4) Four four-phase regions have been confirmed infixed50at.%Zn section of the Al-Zn-Fe-Bi isothermal tetrahedron at600℃, namelyL1+L2+Fe2Al5+α-Fe，L1+L2+α-Fe+δ，L2+α-Fe+δ+Γ and L1+L2+Fe2Al5+FeAl3.(5) In the Al-Zn-Fe-Bi isothermal tetrahedron at600℃, the L1and L2phase are in equilibrium with (Al), FeAl3, Fe2Al5, α-Fe and δ, respectively. No new quaternaryphase is found. The solubility of Zn in FeAl3, Fe2Al5and α-Fe is up to5.1at.%,13.7at.%and8.3at.%, and the solubility of Al in α-Fe, Γ and δ is up to46.7at.%,2.5at.%and2.7at.%. Bi is almost insoluble in the Fe-Al and Fe-Zn compounds. |
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