Microstructure and corrosion resistance of modified 2024 Al alloy using surface mechanical attrition treatment combined with microarc oxidation process

A top ceramic coating was fabricated on the surface mechanical attrition treatment (SMAT) modified nanocrystalline layer of 2024 Al alloy by microarc oxidation (MAO) process. The corrosion resistance of the SMAT-MAO composite coating was studied by EIS. The results show that SMAT-MAO composite coating with 10 μm top ceramic coating exhibited better corrosion resistance, while the SMAT-MAO coating with the thickness of 15 μm showed worse corrosion resistance compared with those simple MAO coatings with same thickness. The formation of a dense passive film at the damaged region caused by the bottom nanocrystalline interface contributed to the improved corrosion resistance property.

Research highlights
► A 20 μm thick nanocrystalline layer with average grain size of 52.8 nm was fabricated on the surface of 2024 Al alloy by means of SMAT.
► A composite coating (named SMAT-MAO coating) was fabricated on the surface mechanical attrition treatment (SMAT) modified nanocrystalline layer of 2024 Al alloy by microarc oxidation (MAO) process.
► SMAT-MAO composite coatings with 10 μm top ceramic coating exhibited better corrosion resistance in comparison with the simple MAO coating with same thickness, while the SMAT-MAO coating with the thickness of 15 μm showed worse corrosion resistance in comparison with that of 15 μm MAO coating.
► The better corrosion resistance of composite coating can be attributed to the formation of a dense passive film at the damaged region caused by the bottom nanocrystalline interface.