Effect of Pre-oxidation Condition on the Microstructure of a Hot-Dip Galvanized Coating on Nodular Cast Iron.

In this paper, the pre-oxidation products, surface silicon content, hot-dip galvanized layer structure and corrosion resistance of nodular cast iron pre-oxidized by sodium bicarbonate were studied by scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction. When the pre-oxidation temperature is 100 °C, the pre-oxidation product is primarily Fe₂O₃. The oxidation products are Fe₂O₃ and SiO₂ at 200 °C and that is mainly SiO₂ at 300 °C. The surface silicon content of the pre-oxidized samples decreases first and then increases with increasing pre-oxidation temperature. The silicon content of samples after alkali and acid washing decreases with increasing pre-oxidation temperature. With the increase in pre-oxidation temperature, the thickness of the alloy layer in the zinc coating of nodular cast iron continuously decreases. The thickness of the alloy layer in the zinc coating of nodular cast iron pre-oxidized at 300 °C is only 37.3 μm, which is 43.9% lower than that of nodular cast iron without pre-oxidation. [ABSTRACT FROM AUTHOR]