Designing the Color of Hot-Dip Galvanized Steel Sheet Through Destructive Light Interference Using a Zn-Ti Liquid Metall
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HOT-DIP galvanizing is a well-established surface coating industrial process with many scientific aspects studied in the past and even today.[1–9] In addition to obvious corrosion requirements, the interest in decorative use of colored coatings has recently increased.[10–12] These two fields have been combined in some patents and research papers.[13–22] Following this line, the goal of the
present paper is to prepare colored coatings on hot-dip galvanized steel sheet using a Zn-Ti bath. As will be proven, color appears due to interference of light on a thin (30 to 80 nm), transparent TiO2 layer, to be formed when the steel sample is removed from the Zn-Ti bath to air. The novelty of this paper is that our experimental findings are supported by a new, complex model, which connects various experimental parameters with the color of the coating. II.
GABOR LEVAI, formerly Ph.D. Student with the University of Miskolc, Egyetemvaros, Miskolc, 3515 Hungary, is now Research Engineer with Innocenter Nonprofit Ltd, 7 Egyetem ut, Miskolc, 3515 Hungary. MELINDA GODZSA´K, Ph.D. Student, and TAMAS I TO¨RO¨K, Professor, are with the University of Miskolc, Egyetemvaros. JOZSEF HAKL and ATTILA CSIK, Senior Researchers, VIKTOR TAKA´TS, Junior Researcher, and KALMAN VAD, Senior Researcher, Head of Department, are with the Institute for Nuclear Research (MTA ATOMKI), 18/c Bem te´r, Debrecen, 4026 Hungary. GEORGE KAPTAY, Professor, is with the University of Miskolc, Egyetemvaros, and also with the Bay Zoltan Ltd, BAYLOGI, 2 Igloi ut, Miskolc, 3519 Hungary. Contact mail: [email protected] Manuscript submitted July 9, 2015. Article published online May 9, 2016 3580—VOLUME 47A, JULY 2016
MATERIALS AND EXPERIMENTAL DETAILS
Low-alloyed steel sheets of type DC01 (St12 according to DIN) were selected in this work (see Table I for chemical composition) to avoid possible interactions with the alloying elements of steel. The dimensions of steel sheets to be coated were 0.8 mm thickness 9 80 mm width 9 100 mm length (the samples were dipped into the Zn-Ti bath along their length). Special High Grade (SHG) zinc was used in this work (see Table II for its chemical composition). One can see that all contaminants were kept at a very low level. In our work, the extremely low levels of aluminum and METALLURGICAL AND MATERIALS TRANSACTIONS A
magnesium were of special importance, as at a higher level, Al and/or Mg might be oxidized preferably instead of Ti, not allowing the formation of TiO2 and its corresponding color on the outer surface of the Zn coating.[20] To alloy liquid zinc with titanium, titanium shavings were used for their high specific surface area to allow fast dissolution into the zinc bath. The chemical composition (see Table III) of the Ti shavings was found by ICP spectrometry (after dissolving them in an aqueous solution), using a 720-ES type equipment of Varian Inc. The calibration solutions were prepared using high-purity titanium and standard solutions Certipur IV of Merck. The Ti shavings were found to contain 1.95 wt pct Si, 0.21
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