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 degrees C, the pre-oxidation product is primarily Fe2O3. The oxidation products are Fe2O3 and SiO2 at 200 degrees C and that is mainly SiO2 at 300 degrees 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 degrees C is only 37.3 mu m, which is 43.9% lower than that of nodular cast iron without pre-oxidation.

Automated summary

This paper studied the pre-oxidation products, surface silicon content, hot-dip galvanized layer structure and corrosion resistance of nodular cast iron pre-oxidized by sodium bicarbonate through scanning electron microscopy, energy-dispersive spectrometry, and X-ray diffraction. It was found that the pre-oxidation product was mainly Fe2O3 at 100 degrees C, Fe2O3 and SiO2 at 200 degrees C, and mainly SiO2 at 300 degrees C. The thickness of the alloy layer in the zinc coating of nodular cast iron continuously decreased with increasing pre-oxidation temperature, and the thickness of the alloy layer at 300 degrees C was 43.9% lower than that without pre-oxidation.