Effect of Fe3+ ions on the thermal and optical properties of the ceramic coating grown in-situ on AZ31 Mg Alloy

This research investigates the effect of Fe2(SO4)3 on the thermal and optical properties of the ceramic coatings formed on AZ31 Mg alloy. The different ceramic coatings were obtained by plasma electrolytic oxidation (PEO) in electrolytes that contain varied concentrations of Fe2(SO4)3. The microstructure, element distribution, composition as well as the thermal and optical properties of the coatings were studied with scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), UV–VIS–NIR spectrophotometer and infrared reflectometer. The results show that all of the coatings prepared were mainly composed with MgO, with trace-amount of Fe3O4 presents and Fe seems entered into the MgO crystal structure. With the increasing of the concentration of Fe2(SO4)3, the solar absorptance and infrared emittance increased initially but then remain stable. We found that at the concentrations 8 g L−1, the coating has the highest solar absorptance (0.94) and infrared emittance (0.83). Our results show that coatings formed with this method could be useful as a thermal control coating in a variety of applications, such as in the spacecraft.

► Thermal control coatings on AZ31 Mg alloy were prepared by the plasma electrolytic oxidation (PEO) method.
► The coatings were mainly composed with MgO, with trace-amount of Fe3O4 presents.
► The using of Fe3+ in the electrolyte improves the thermal and optical properties of the obtained MgO coating.
► The thermal control coating obtained by PEO has high solar absorptance (0.94) and infrared emittance (0.83).