Ceramic coatings were prepared on 6061 aluminum alloy in electrolytes containing La2O3 particles using the micro-arc oxidation technique. The main work focuses on the microstructure, phase composition, elemental distribution and corrosion resistance of micro-arc oxidation coatings. The results showed that the addition of La2O3 increased the oxidation voltage and promoted the formation rate. Scanning electron microscopy observations indicated that the quantity of discharge micropores decreased and the thickness increased, and thus, the microhardness increased. The X-ray diffraction results showed that the coatings mainly consisted of γ-Al2O3, α-Al2O3 and SiO2. Electrochemical corrosion tests showed that the corrosion resistance of the coated sample with La2O3 increased greatly because the addition of La2O3 significantly reduced the micropores of the coating surface and made the coating thicker, smoother and harder. Hence, the addition of La2O3 can optimize the structure of the micro-arc oxidation coating and improve its corrosion resistance.

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Rare earth salt SmCl3 was added to the electrolyte to improve the corrosion performance of the AZ91D magnesium alloy plasma electrolytic oxidation (PEO) coating. The influence of SmCl3 on coating formation, morphology and performance was investigated. The results showed that adding SmCl3 can not only refine the discharge holes but also improve the coating's formation efficiency and its’ combination with the substrate. Potentiodynamic polarisation (PDS) and electrochemical impedance spectroscopy (EIS) tests showed that the corrosion characteristics of the PEO coating were greatly improved with SmCl3's addition. The corrosion current density decreased from 8.208 × 10−4 to 3.733 × 10−8 A cm−2 when the presence of optimum level of SmCl3 in solution (0.25 g L−1). Cyclic polarisation test indicated that the pitting corrosion of AZ92D was improved.