Reactions of FeCr alloys with liquid zinc in hot-dip galvanizing

• Interfacial reactions in α-(Fe,Cr)/Zn couples at 450 °C were investigated.
• Simply layered structure was observed in Fe–5Cr/Zn and Fe–95Cr/Zn diffusion couples.
• Alternating layers were found in Fe–30Cr/Zn and Fe–70Cr/Zn diffusion couples.
• Thermodynamic foundation and mechanism of the formation of the alternating layers are elaborated.

This study investigates reactions of FeCr alloys (containing 5, 30, 70 and 95 at.% Cr) with liquid zinc for annealing times up to 1224 h. Simple layered structure was observed at interfaces of Fe–5Cr/Zn and Fe–95Cr/Zn. However, alternating layers were found at interfaces of Fe–30Cr/Zn and Fe–70Cr/Zn. Thickness of the alternating layers varies linearly with square root of time, indicating that growth kinetic of the alternating layers is a diffusion controlled process. Periodic thermodynamic instability at the Fe–30Cr/(Cr) or Fe–70Cr/(Cr) interface causes the subsequent nucleation of new alternating layer pairs. The thermodynamic foundation and mechanism of formation of the alternating layers are elaborated in this paper.