Al-Fe-Zn (Aluminum-Iron-Zinc)
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hase Diagram Evaluations: Section II
Al-Fe-Zn (Aluminum-Iron-Zinc) V. Raghavan
The early results on this ternary system were reviewed by [1992Rag]. An update on the phase equilibria of Zn-rich alloys by [2003Rag] presented an isothermal section at 450 C for metastable and stable equilibria from [1992Per] and two sections at 470 and 440 C from [1995Yam]. A full thermodynamic description of this system was reported subsequently by [2007Nak], who used in the optimization the activities derived from their own emf measurements, as well as those of [1995Yam, 1998Yam] and the new results of [2007McD]. The computed phase equilibria from [2007Nak] were briefly reviewed in the update of [2008Rag]. At about the same time that the paper of [2007Nak] was published, [2007McD] reported new experimental results and computed the phase equilibria in Zn-rich alloys in the temperature range of interest in the galvanizing processes. Here, the results of [2007McD] and [2007Nak] will be compared.
phases are: C (Fe3 Zn10 ; Cu5 Zn8 -type cubic), C1 (Fe11 Zn40 ; cubic), d (FeZn10 -type hexagonal) and f (CoZn13 -type monoclinic).
Ternary Isothermal Sections With starting metals of 99.99% Al, 99.99% Fe and special high-grade Zn, [2007McD] added to a 20-kg bath of molten Zn chopped wire pieces of Al and Fe in a controlled atmosphere of dry N2. The Al concentration was varied between 0.09 and 0.25 mass% and the melt was kept
Binary Systems The Al-Fe phase diagram depicts several intermediate phases. Apart from the high temperature phase Fe4 Al5 (e), there are three phases stable down to room temperature: FeAl2 (triclinic), Fe2 Al5 (70-73 at.% Al; orthorhombic) and Fe4 Al13 (74.5-76.6 at.% Al; monoclinic). The Al-Zn phase diagram depicts a eutectic reaction at 381 C between (Al) and (Zn). In the (Al) region, a miscibility gap occurs in the solid state with the critical temperature at 351:5 C and the monotectoid reaction at 277 C. There are no intermediate phases in this system. In the Fe-Zn system, the intermediate
Fig. 2 Al-Fe-Zn computed metastable isothermal section at 470 C
Fig. 1 Al-Fe-Zn computed metastable isothermal section at 480 C
Fig. 3 Al-Fe-Zn computed metastable isothermal section at 460 C
Journal of Phase Equilibria and Diffusion Vol. 32 No. 2 2011
143
Section II: Phase Diagram Evaluations system. The phase equilibria in the Zn-rich corner were calculated by extrapolation of the binary parameters. The calculated phase boundaries showed good agreement with their own experimental measurements. In Fig. 1-4, the computed isothermal sections of [2007McD] at the Zn-rich corner are shown. For clarity, the experimental data points are omitted. Also, in Fig. 1-4, the computed isothermal sections of [2007Nak] are superimposed for comparison. The two sets of calculated equilibria are not quite in agreement, especially at lower Al contents. Since the description of [2007Nak] is based on the standard CALPHAD technique and is applicable over the entire composition range, it may be preferred.
References Fig. 4 Al-Fe-Zn
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