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.