Enhanced corrosion resistance of magnesium alloy by plasma electrolytic oxidation plus hydrothermal treatment

Abstract

Plasma electrolytic oxidation (PEO) is a promising surface treatment technique to enhance the corrosion resistance of Mg alloy . However, the micro-pores and micro-cracks of the PEO coating limit its anti-corrosion protection capability. In this study, a dense Ca 3 Al 2 (OH) 12 layer was fabricated on the PEO coating surface by hydrothermal treatment (HT), forming a PEO/HT composite coating . Surface morphologies , chemical composition, phase composition and growth process of the PEO/HT composite coating were characterized using Field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectrophotometer (FT-IR). Corrosion resistance of the samples was studied through immersion test, hydrogen evolution test, and electrochemical test. Results demonstrated that the PEO/HT coating possessed a polyhedral structure and the micro-pores and micro-cracks of the PEO coating were sealed. The PEO/HT composite coating showed improved bioactivity in comparison with PEO coating and Mg alloy after immersion in Hanks' solution. Moreover, the Ca 3 Al 2 (OH) 12 crystals layer improved the corrosion resistance of PEO coating significantly. Furthermore, the growth process of Ca 3 Al 2 (OH) 12 layer was discussed. • A dense Ca 3 Al 2 (OH) 12 layer was fabricated on the PEO coating surface by HT. • The anti-corrosion property of the PEO/HT coating was significantly higher than that of both Mg alloy and PEO coating. • The formation mechanism of Ca 3 Al 2 (OH) 12 structure layer was proposed.