Influence of silicon on the a-Fe/F interface of hot-dip galvanized steels

• Published in: Surface & coatings technology Vol. 200; no. 18-19; pp. 5277 - 5281
• Main Authors: Jintang, Lu, Chunshan, Che, Gang, Kong, Qiaoyu, Xu, Jinhong, Chen
• Format: Journal Article
• Language: English
• Published: 08.05.2006
• ISSN: 0257-8972
• DOI: 10.1016/j.surfcoat.2005.06.017

After steel sheets (0.37 wt.% Si) pre-electroplated with a thin layer of pure Fe were immersed in molten zinc for various times, the change in the microstructure of the galvanized coating on the steel and the change of the alpha-Fe/F interface were studied. The EDS results show that excessive silicon accumulates on the surface of the steel substrate due to the low solubility of silicon in the F layer after the Fe layer is depleted by the increasing growth of Fe-Zn compound layers. With the movement of the alpha-Fe/F interface towards the substrate by the Fe/Zn reaction, silicon-rich a-Fe peels off from the substrate and breaks into particles. The particles, much like an inert marker in a Kirkendall effect experiment, move towards the delta layer through the F layer because silicon-rich alpha-Fe cannot be adsorbed in the F layer. On reaching the delta/F interface, the particles quickly dissolve in the delta layer, and accelerate its growth towards the steel substrate, resulting in the gradual disappearance of the F layer. At the same time, the continuous and compact coating is quickly changed into the loose and overly-thick one as silicon dissolved in the 6 layer soon diffuses toward the layer.