Studies of the morphology of the al-rich interfacial layer formed during the hot dip galvanizing of steel sheet

A small addition of Al in the liquid Zn bath inhibits the Fe/Zn reactions during hot dip galvanizing of steel sheets. Although it is well known that Al and Fe are tied up in a layer located at the interface between Fe and Zn, the effect of the galvanizing parameters on the formation of this Al-rich...

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Bibliographic Details
Published in:Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 1999-03, Vol.30 (3A), p.681-695
Main Authors: BARIL, E, L'ESPERANCE, G
Format: Article
Language:English
Subjects:
Applied sciences
Exact sciences and technology
Metallic coatings
Metals. Metallurgy
Production techniques
Surface treatment
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Summary:A small addition of Al in the liquid Zn bath inhibits the Fe/Zn reactions during hot dip galvanizing of steel sheets. Although it is well known that Al and Fe are tied up in a layer located at the interface between Fe and Zn, the effect of the galvanizing parameters on the formation of this Al-rich interfacial layer is not known. This study has been carried out to determine the effect of the galvanizing parameters on the formation of this Al-rich layer. Five zinc baths containing 0.10, 0.12, 0.13, 0.16, and 0.18 wt.% Al were used to produce galvanized coatings of commercial ultra-low-carbon (ULC) steel substrate. Full inhibition of the Fe /Zn reactions was achieved in baths with Al content > 0.15 wt.%. The Al-rich layer is isomorphous to Fe sub 2 Al sub 5 crystals and the Fe/Al ratio is close to Fe sub 2 Al sub 5 with large amounts of Zn present (22-28 wt.%). The morphology of the Al-rich layer is strongly related to the Al content of the bath. Indeed, bath contents > 0.15 wt.% are associated with two sublayers of Fe sub 2 Al sub 5 crystals, making up colonies of grains of similar crystallographic orientation and directly associated to the crystallographic orientation of the steel grains. In baths with contents < 0.15 wt.%, the Al-rich layer has only one sublayer of crystals and shows colonies of grains with similar orientation. Finally, the Fe sub 2 Al sub 5 crystals have a strong crystallographic texture. X-ray diffraction (XRD) reveals that the (200) planes are parallel to the surface of the substrate.
ISSN:1073-5623
1543-1940
DOI:10.1007/s11661-999-0060-6