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The microstructure of 55 w/o Al—Zn—Si (Galvalume) hot dip coatings

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Journal of Materials Engineering

Abstract

Light metallography, x-ray diffraction, scanning electron microscope (SEM), (EMPA), and scanning transmission electron microscope (STEM) were used to study the microstructural characteristics of 55 w/o Al—Zn-Si (Galvalume) hot-dip coatings on steel. Processing variables of coating thickness and dip time were studied and a thin foil sample preparation technique involving ion beam thinning for the STEM evaluation of coating cross sections was developed. The spangled coating surface was comprised of a fine dendritic network, and correlations between dendrite arm spacing and spangle size with coating thickness have been made. The overlay, or solidified bath, consists of grains of A1-rich dendrites along with Zn-rich interdendritic zones. EMPA in conjunction with TEM imaging showed that these Zn-rich interdendritic regions had a heavy concentration of precipitates. Selective etching of the overlay revealed a forest of Si particles which grew out from the alloy layer. The alloy layer was studied using the EMPA and STEM and it was found that up to five intermetallic phases were present after long dip times.

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Authors and Affiliations

  1. Lehigh University, Bethlehem, PA

    J. H. Selverian, M. R. Notis & A. R. Marder

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  1. J. H. Selverian
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  2. M. R. Notis
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  3. A. R. Marder
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Selverian, J.H., Notis, M.R. & Marder, A.R. The microstructure of 55 w/o Al—Zn—Si (Galvalume) hot dip coatings. J. Mater. Eng. 9, 133–140 (1987). https://doi.org/10.1007/BF02833702

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  • DOI: https://doi.org/10.1007/BF02833702

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