The pore structure and properties of microarc oxidation films on 2024 aluminum alloy prepared in electrolytes with oxide nanoparticles

Microarc oxidation films on 2024 aluminium alloy were prepared in sodium silicate-based electrolyte with α-Al2O3, SiC, TiO2, ZrO2 and CeO2 nanoparticles. The effects of oxide nanoparticles on the pore parameters and the properties of the films were studied. EDS and XRD analysis showed that the nanoparticles partly entered the film, probably by the combination effects of embedding and melting. The porosity of the microarc oxidation films prepared in electrolytes with nanoparticles increased to some extent. With the addition of the different nanoparticles, the film porosity increased from 9.6% to 21.6%, the bonding strength of the films to the adhesives increased from 12.3 MPa to 22.8 MPa, and the film microhardness decreased from 785.7 HV to 564.2 HV. Particularly, the microhardness of the film prepared with SiC nanoparticles was as high as 1063.5 HV. The addition of all the nanoparticles into the electrolytes did not affect the thermal cracking resistance of the films. EIS measurements showed that after 1440 h immersion in NaCl solution the resistance of the microarc oxidation films prepared in electrolyte with nanoparticles was still much higher than that of the original film, and the film capacity increased slowly. Among the nanoparticles, TiO2 and CeO2 showed the best effect to increase the corrosion resistance. Weight loss test results showed that the corrosion rate of the films prepared with TiO2 and CeO2 nanoparticles was only about one third of the original film after 8640 h immersion. The good corrosion resistance of the microarc oxidation films may depend mainly on the good shielding property of the inner compact layer. •The nanoparticles enter the microarc oxidation films probably by the combination effects of embedding and melting.•The porosity of the films prepared in electrolytes with nanoparticles increases obviously.•With the increased film porosity, the bonding strength of the films to the adhesives increases and the film microhardness decreases.•The addition of the nanoparticles does not affect the thermal cracking resistance of the films.•The good corrosion resistance of the films depends mainly on the good shielding property of the inner compact layer.