Abstract:Sol-gel coatings containing various amounts of hydroxylated nanodiamond (HND) particles were applied on the magnesium alloy for corrosion protection. The micrometric defects in the sol-gel coating completely disappeared after adding 0.01, 0.02 and 0.05 wt.% of the HND nanoparticles. The AFM analyses showed that average roughness of the sol-gel film is about 6.7 nm which increases to 16.1 and 20.2 nm after incorporating 0.005 and 0.02 wt.% of the HNDs, respectively. The corrosion resistance of the coatings was tested in Harrison’s solution by means of EIS technique after 15, 30, 60 and 120 min immersion. The corrosion resistance of the sol-gel coating was remarkably enhanced by incorporating different contents of the HNDs and the best result was obtained for 0.01 wt.%. The results of the EIS experiments were confirmed by the potentiodynamic polarization tests. The corrosion resistance enhancement was attributed to the film compactness (due to the chemical interaction with the HNDs), formation of tortuous pathways for diffusion of the corrosive solution, and filling of the defects by the nanoparticles. However, the beneficial effect of the HNDs on the corrosion resistance gradually diminished as the content of nanoparticle was increased. Finally, the micromorphology of the sol-gel nanocomposites was studied after the corrosion tests.

Key words: magnesium alloy; corrosion; coating; sol-gel; nanodiamond