Interfacial Investigation of St13/Molten Zn–5% Al and Corrosion Behavior of Formed Layer via Hot-Dip Process

Abstract

In the present study, the effect of temperature and duration of hot-dipping on structural properties, hardness, and corrosion resistance of Zn–5% Al coatings on ST13 low-carbon steel has been investigated. The samples were dipped in a molten metal bath at temperatures of 440, 480 and 520°C, during 20, 50 and 70 seconds. To investigate the microstructure and properties of samples, scanning electron microscopy, energy dispersive X-ray spectrometry, microhardness measurements, and potentiodynamic polarization corrosion tests were used. The results showed that the coating structure is an eutectic layer at 440°C, and at the interface of the substrate and the coating a thin inhibitory layer is formed that prevents the diffusion of the substrate atoms into the coating and from the molten bath into the substrate. With an increase of temperature to 480 and 520°C, with the diffusion of iron atoms of the substrate and of the molten bath, a triple metallic layer of Al–Fe–Zn forms, and the thickness of the coating increases. As the dipping time increases, the number of intermetallic particles in the coating also increases. At higher temperatures, the hardness went up from 86 to 121.73 Hv and the corrosion rate—from 7.381 to 37.53 Mpy. hot dip, Zn–5% Al coating, microstructure, intermetallic, corrosion