Al alloy protection via ultra-thin ceramic coatings and different surface pretreatments

The efficiency of ultra-thin corrosion protection coatings for susceptible to local corrosion AA2024-T3 is demonstrated. For this purpose, with atomic layer deposition (ALD) 50 nm thick TiO2, Al2O3, an Al2O3-TiO2 mixture and Al2O3/TiO2 nanolaminate coatings are grown on AA2024-T3 substrates, receiving different pretreatments prior to ALD coating. One pretreatment involves polishing and cleaning with organic solvents, and the second utilizes an additional low-potential electrochemical treatment in sulfuric acid. The samples are characterized with scanning electron microscopy, scanning transmission electron microscopy, wavelength-dispersive X-ray fluorescence spectroscopy, X-ray diffraction and reflection, and nanoindentation and are tested using linear sweep voltammetry, electrochemical impedance spectroscopy, and immersion in a salt solution. The study shows that ultrathin metal oxide coatings applied via ALD can significantly enhance the corrosion resistance of Al alloys, and the performance depends on the pretreatment of the alloy, as well as on the material/structure of the coating. The best ultrathin coating with less than 100 nm thickness withstood well 1000 h immersion test. [Display omitted] •Low-potential electrochemical pretreatment creates a thin Al2O3 layer on Al-alloy.•Corrosion protection of Al2O3/TiO2 laminate is superior to the oxides and mixture.•Electrochemical pretreatment enhances the protection of the nanolaminate coating.•The pretreatment avoids rapid local corrosion of an uncoated Al-alloy substrate.•ALD nanolaminates are stronger than the oxides and their mixture nanofilms.