Reactive Wetting of an Iron-Base Superalloy MSA2020 and 316L Stainless Steel by Molten Zinc-Aluminum Alloy
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CORROSION and erosion of pot hardware by molten Zn-Al alloy have long been an issue of concern in the galvanizing processing industry.[1–6] The formation of intermetallic phases by reaction between the metallic hardware and galvanizing media would aggravate the dross buildup on the pot rolls and bearings and, thus, reduce the service life of the pot hardware. Frequent line stoppages for maintenance are required to avoid impairment to the coating quality as a result of excessive dross formation. Therefore, extensive research efforts have been conducted to examine the reaction of molten Zn-Al alloy baths with various materials, including ceramics, cermet, steel, and superalloys.[7] The wettability of solids by liquid metals at high temperature carries important implications of interfacial reaction mechanisms for liquid/solid contact.[8] The reactive wetting behaviors of steels in molten Zn-Al baths have been well examined by attempts to evaluate the effectiveness of the galvanizing processes. In particular, it was found by Brondyke that progressive wetting and subsequent penetration of Al-Si carbide materials by molten Al at 700 C to 1000 C gave rise to reactive JING XU, Graduate Research Assistant, XINGBO LIU, Assistant Professor, and EVER BARBERO, Professor, are with the Mechanical & Aerospace Engineering Department, West Virginia University, Morgantown, WV 26506. Contact e-mail: [email protected] MARK A. BRIGHT, Technology Manager, is with the Metallics Systems (Division of Pyrotek Incorporated), Solon, OH 44139. JAMES G. HEMRICK, Staff Member, and VINOD SIKKA, Manager, are with the Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831. Manuscript submitted August 29, 2007. Article published online April 2, 2008 1382—VOLUME 39A, JUNE 2008
product buildup and tensile stress formation.[9] As for galvanizing high-strength steel in molten Zn-Al alloy, a study by Bordignon indicated selective oxidation of segregated Mn and Si at 800 C during annealing before hot dipping reduced wettability and reactivity of molten zinc and aluminum on free iron at 460 C. Additionally, the presence of nonoxidizable constituents such as Sn and P improved wettability by reducing preferential oxidation.[10] Through a similar research project, Giorgi et al. further pointed out the variance of selective oxidation from segregated constituents as a result of inconsistencies in annealing time and temperature and the consequential impact on reactive wetting, as determined by sessile drop measurements.[11] Gradual improvement of the contact angle with time between a silicon-bearing steel and zinc at 470 C has been observed by Chung et al.[12] The complete coverage of the steel surface by a zinc droplet 20 minutes after dipping indicates the rate-limiting reaction kinetics. In distinctive contrast, a dynamic-dominant wetting behavior has been found for dip coating of low-carbon steel with Al-Zn-Si alloy melts by Ebrill et al.[13] The contact angle displays an abrupt transition from nonwetting
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