Abstract
MgO coatings were electrodeposited on Mg alloy substrates via cathodic electrolytic technique and annealed at different temperatures. The protective performance of these annealed coatings was investigated, and a correlation drawn between annealing temperature of coatings and their corrosion resistances as well as mechanical hardness. At optimum temperature (250 °C), the thermal treatment relieved internal tensile stress leading to crystallization of oxide coating layers with compact and continuous multilayered microstructures. At higher temperatures (around 500 °C), phase transformations within the coating microstructure broadened inherent inter-diffusion pathways/microdefects. Surface and bulk evidences of pores and cracks are observed at 500 °C as clear evidences of the consequence of over-calcination using scanning electron microscopy. Enhanced corrosion resistance for coatings are achieved at optimum curing temperature judging from electrochemical corrosion results after chloride-induced corrosion tests. The dependence of corrosion resistance on annealing temperature of coatings has also been investigated by potentiodynamic polarization and electrochemical impedance spectroscopic techniques. A modelled curing mechanism, as it relates to barrier performance at low and high thermal conditions, has been illustrated from experimental evidences.
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