Effect of orientation and lamellar spacing of Fe2B on interfaces and corrosion behavior of Fe-B alloy in hot-dip galvanization

The effects of orientation and lamellar spacing on the interface microstructure and corrosion behavior of a directionally solidified (DS) Fe-B alloy in a hot-dip galvanization bath were investigated. The results indicated that the microstructure of the DS Fe-B alloy consisted of oriented α-Fe and Fe2B grains. The oriented Fe2B with [002] preferred growth orientation displayed low-angle grain boundaries on the Fe2B (001) basal plane. The DS Fe-B alloy with Fe2B vertical to the corrosion interface possessed the best corrosion resistance to liquid zinc owing to the formation of an interface-pinning multilayer induced by the Fe2B orientation. The epitaxially grown columnar ζ-FeZn13 products were controlled by the geometric constraint of Fe2B grain orientation and size, and a mechanism model that explains the interfacial orientation-pinning behavior is discussed in detail. Transmission electron microscopy (TEM) results revealed that the possible orientation relationships of the oriented Fe2B and columnar ζ-FeZn13 products are (001)Fe2B//(−402)ζ-FeZn13 and [002]Fe2B//[110]ζ-FeZn13. The corrosion damage of the DS Fe-B alloy with Fe2B [002] orientation vertical to the corrosion interface in liquid zinc was governed by the competitive mechanisms of Fe2B/FeB transformation and microcrack-spallation resistance, which is proposed as being the result of a multiphase synergistic effect in the micro-structures. [Display omitted]