Abstract: A duplex process was designed to modify the surface of LY12 CZ aluminum alloy by using surface mechanical attrition treatment(SMAT) prior to microarc oxidation(MAO). A surface nanocrystalline(SNC) layer was formed on the alloy surface by SMAT,a ceramic outer layer grew on the SNC layer by MAO,and finally an SNC-MAO composite coating was fabricated. The tribological behaviors of the MAO coating and SNC-MAO composite coating were comparatively evaluated. Experimental results showed that the SNC-MAO composite coating had a better wear resistance than the MAO coating in the same test condition due to a higher hardness of the ceramic coating. The wear mechanism of the MAO coating and SNC-MAO composite coating involved materials transfer from the steel ball to the coating and oxidation wear.