Transformation of Fe–Al phase to Fe–Zn phase on pure iron during galvanizing

Focussing on a nucleation site of Fe–Zn intermetallics, phase transformation of Fe–Al intermetallics to Fe–Zn intermetallics in galvanized coatings are studied by combined ECP–SEM techniques. This study sheds new light on the effects of retained Fe–Al intermetallics on the orientation relationship of Fe–Zn intermetallics with respect to substrates. Pure iron substrates are galvanized using 0.20 mass%Al-bearing molten zinc bath. The parent high Al galvanized coatings are subsequently annealed using a molten salt bath kept at 430°C, followed by water quenching. The Fe–Al phase formed during galvanizing shows no effect on the orientation relationship between a FeZn13(ζ) phase formed during galvannealing and an underlying substrate. Based on this result, and in conjunction with published reports by others, the nucleation mechanism of Fe–Zn intermetallics in high aluminum coatings is discussed.