Formation of Fe₂Al₅ Phase Layer on Fe-Si Alloy Sheets Hot-Dipped in Zn-0.2Al Alloy Melt

Abstract

We have characterized η-Fe₂Al₅ phase layers formed on Fe-Si binary alloys (pure Fe, Fe-0.2Si and Fe-1Si (wt%)) hot-dipped in a Zn-0.2Al (wt%) alloy melt at 460ºC for various times ranging from 2 to 3600 s. The Al addition in the Zn melt suppressed the interfacial reaction between liquid Zn and α-Fe phase with Si in solution. At an early stage of dipping (less than 10 s), Fe dissolution into the Zn-0.2Al alloy melt occurs more significantly on the α-Fe phase with higher Si content. The thickness of Fe₂Al₅ phase layer becomes slightly larger on α-Fe phase with higher Si content. These indicates that solute Si in α-Fe phase could enhance the Fe dissolution providing the driving force for the formation of η phase in liquid Zn alloy, resulting in the enhanced formation of η phase layer. The thicker η phase layer formed on Fe-Si alloy sheets would play a role of diffusion barrier, resulting in the suppression of subsequent interfacial reactions even after 3600 s in dipping.