In this study, plasma electrolytic oxidation (PEO) of Ti–Mg couple metal fabricated by friction stir welding (FSW) in silicate base solution has been addressed and effect of silicate concentration in the electrolyte on coating properties was studied. Microstructure, composition and corrosion resistance of coating were characterized using scanning electron microscopy(SEM), x-ray diffraction (XRD) and potentiodynamic polarization methods. Ti–Mg couple were successfully coated simultaneously in silicate electrolyte and results of this study indicated that silicate concentration has a considerable impact on microstructure and corrosion resistance of the coating. In 5 g l−1 sodium silicate concentration the lower thickness leads to higher microspores on surface and consequently lower corrosion resistance of fabricated coating and at 15 g l−1 sodium silicate concentration, higher coating thickness leads to a decrease in the number of the pores and increase the pore diameter and consequently the corrosion resistance of the coating is deteriorated in these conditions. Results showed that the best corrosion resistance is obtained in the 10 g l−1 sodium silicate concentration due to high uniformity of coating. Results of XRD analysis indicated that, Mg2SiO4, MgSiO3, MgF2 and MgO and formed on Mg. And rutile, anatase, and SiO2 amorphous phase were formed on Ti.

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