Influence of Aluminum on the Formation Behavior of Zn-Al-Fe Intermetallic Particles in a Zinc Bath
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ZINC coatings are used predominantly to improve the aqueous corrosion of steel by providing barrier protection as well as galvanic protection. One typical processing method used in producing Zn coatings is hotdip galvanizing, i.e., the immersion of a steel sheet in a liquid bath of Zn or Zn alloy, by batch or continuous processing, the latter being more advantageous for coiled products.[1] The growing importance of hot-dip galvanized coatings on automotive parts has led in recent years to studies on the mechanisms of their formation on interstitial-free (IF) steel substrates as well as high strength transformation-induced plasticity (TRIP) aided steels and twinning-induced plasticity (TWIP) aided steels of high strength and good formability.[2–12] JOO HYUN PARK, Professor, is with the School of Materials Science and Engineering, University of Ulsan, Ulsan 680-749, Korea. Contact e-mail: [email protected] GEUN-HO PARK, formerly Graduate Student, with the School of Materials Science and Engineering, University of Ulsan, now is with the Steelmaking Technology Development Team, Technical Research Center, Hyundai Steel Company, Dangjin, Chungnam 167-32, Korea. DOO-JIN PAIK, Manager, and MOON-HI HONG, Project Manager, are with the Surface Treatment Department, POSCO, Gwangyang, Jeonnam 545-711, Korea. YOON HUH, Senior Researcher, is with the Department of Analysis and Assessment, Research Institute of Industrial Science and Technology (RIST), Pohang 790-330, Korea. Manuscript submitted March 26, 2011. Article published online August 19, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
Dross in the Zn pot can be classified by oxide type (Zn and/or Al) and intermetallic compound type (Zn-Fe and Fe-Al). The latter type tends to cause dross problems and forms in the Zn pot when Al and Fe are present in concentrations above the solubility limits.[1,13–18] Specifically, problematic intermetallic compounds have been identified as Fe2Al5Znx (g phase) ‘‘top’’ or ‘‘floating’’ dross as well as FeZn7 (d1 phase), FeZn10Alx (d phase), and FeZn13 (f phase) ‘‘bottom’’ dross particles.[1,19] Several studies investigated the phase equilibria of Zn-Al-Fe ternary systems, as well as stable and metastable phases in dross formation.[20–31] Two valuable studies on phase diagrams of the Zn-Al-Fe system by experimental and computational (CALPHAD) methodologies were published.[28,29] In the work of Nakano et al.,[29] the Zn-rich portion of the Zn-Al-Fe phase diagram at full equilibrium [723 K (450 C)], which included the C2 phase (presumably isomorphic with the C1 phase), was evaluated. Yamaguchi et al. also constructed integrated stable (equilibrium) and metastable potential diagrams for the Zn-Al-Fe system based on the EMF measurement technique.[20–22,31] The C1 (Fe5Zn21) phase was absent in the metastable potential diagram. Recently, Tang reported practical applications of phase equilibria in continuous galvanizing processes including the determination of effective Al content and its consumption, predictions of bath temperature and charact
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