The effect of surface preparation prior to cerium treatment on the corrosion protection of AA6061 T6-10% Al2O3 in NaCl solution was investigated using electrochemical impedance spectroscopy and DC polarization techniques. A new surface preparation method consisted of pre-etching followed by oxide-thickening is proposed. Optical microscope and scanning electron microscopy showed a marked decrease in the number and depth of pits for the pre-etched as compared to the as-polished specimens. X-ray photoelectron spectroscopy revealed that pre-etching eliminated the active sites where the chloride ions can adsorb. Simultaneously, the adsorption of cerium ions is uniformly on the surface. The oxide-thickening step has a vital role in the protection mechanism. It was found that presence of a thick oxide layer completely changed the mechanism of protection.