Growth behaviour of low-energy plasma electrolytic oxidation coatings on a magnesium alloy

Abstract

Plasma electrolytic oxidation (PEO), a promising surface treatment method to improve the corrosion and wear resistance of magnesium and its alloys, operates at high voltages, resulting in a relatively high energy cost. To make the PEO process more economically viable, its energy efficiency needs to be improved. This study investigates the growth behaviour and microstructural characteristics of low-energy PEO coatings on an AM50 magnesium alloy in a concentrated electrolyte containing sodium tetraborate. The surface morphology of the coatings was different from typical PEO coating morphologies and a large voltage oscillation was observed during treatment. Using different characterisation techniques, and based on a micro-discharge model, a correlation was made between the voltage-time behaviour, micro-discharge characteristics and the composition and microstructure of the coated samples. The results suggest electrolyte chemistry can somewhat control discharge behaviour, which plays an important role in PEO coating growth. Keywords: Plasma electrolytic oxidation, Magnesium, Oxide coating, Mechanism, Low energy