A double layer Rare Earth Metal (REM) conversion coating process of Al 6061/SiCp metal matrix composites (MMC) was studied.The corrosion resistance of REM conversion coating was examined by electrochemical impedance spectroscopy (EIS).REM conversion coating produced very corrosion resistant surface of Al 6061/SiCp MMC.The X ray diffraction (XRD) analysis revealed that REM conversion coatings exhibited non crystalline structure.The composition of REM conversion coating was studied by X ray photoelectron spectroscopy (XPS).The coatings consisted of cerium oxide and hydrated cerium oxide.Some of Ce3+were oxidized to Ce4+during the formation of the first layer coating in the solution containing Ce3+.During the course of exposing the specimens in open air,some of the residual Ce3+were oxidized to Ce4+.REM conversion coating formed in the solution containing Ce4+consisted entirely of Ce4+compounds. A double layer Rare Earth Metal (REM) conversion coating process of Al 6061 / SiCp metal matrix composites (MMC) was studied. The corrosion resistance of REM conversion coating was examined by electrochemical impedance spectroscopy (EIS) surface of Al 6061 / SiCp MMC. X-ray diffraction (XRD) analysis revealed that REM conversion coatings exhibit non crystalline structure. The composition of REM conversion coating was studied by X ray photoelectron spectroscopy (XPS). The coatings consisted of cerium oxide and hydrated cerium oxide. Ce of Ce3 + were oxidized to Ce4 + during the formation of the first layer coating in the solution containing Ce3 + .During the course of exposing the specimens in open air, some of the residual Ce3 + were oxidized to Ce4 + .REM conversion coating formed in the solution containing Ce4 + consisted of entirely Ce4 + compounds.