Phase transitions of plasma sprayed Fe–Al intermetallic coating during corrosion in molten zinc at 640 °C

Fe–Al intermetallic coating was prepared on steel substrate by plasma spraying. The corrosion behavior of the Fe–Al coating in molten zinc at 640 °C was investigated in detail. The results showed that the plasma spraying Fe–Al coating was composed of FeAl and (Fe2Al5 + FeAl2) eutectic structure. In the molten zinc corrosion process, (Fe2Al5 + FeAl2) eutectic structure was corroded preferentially. FeAl2 disappeared in the initial stage of corrosion. The phase transition process of Fe2Al5 induced by molten zinc corrosion was Fe2Al5 → Fe2Al5Znx(η) → η + L (liquid phase) → η + δ(FeZn7) + L → L. And the phase transition process of FeAl induced by molten zinc corrosion was FeAl → FeAlZnx → δ+FeAlZnx → δ + α + Γ(Fe3Zn10) → δ + Γ → δ+L → L. The order of corrosion resistance of FeAl2, FeAl and Fe2Al5 against 640 °C molten zinc was FeAl > Fe2Al5 > FeAl2. The results may provide us a useful guide to design Fe–Al intermetallic coating with high corrosion resistance.

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► The Fe–Al coating was composed of FeAl and (Fe2Al5 + FeAl2) eutectic structure.
► (Fe2Al5 + FeAl2) eutectic structure was corroded preferentially by the molten zinc.
► Fe2Al5 phase transition: Fe2Al5 → Fe2Al5Znx(η) → η + L(liquid phase) → η + δ(FeZn7) + L → L.
► FeAl phase transition: FeAl → FeAlZnx → δ + FeAlZnx → δ + α + Γ(Fe3Zn10) → δ + Γ → δ + L → L.
► The order of corrosion resistance against 640 °C molten zinc was FeAl > Fe2Al5 > FeAl2.