Plasma electrolytic oxidation of cold spray kinetically metallized CNT-Al coating on AZ91-Mg alloy: Evaluation of mechanical and surficial characteristics

Abstract

The cold-spray kinetically metallized (CS) carbon nanotube-aluminum (CNT-Al) and pure Al coatings were treated using plasma electrolytic oxidation (PEO) process to obtain CNT-Al+PEO and Al+PEO duplex coatings on AZ91 Mg alloy, respectively. The phase composition, microstructure, mechanical properties, wear and corrosion resistance of the PEO ceramic coatings were studied. The results showed that the PEO ceramic coating was mainly composed of α-Al2O3 and γ-Al2O3, moreover, the small amount of CNT was also retained during the PEO process. The mechanical properties and wear resistance of the PEO ceramic coatings were significantly improved compared to the respective CS coatings. In particular, the hardness and elastic modulus of the PEO-CNT coating reached 13.9 GPa and 185.4 GPa, which were 21.0% and 23.4% higher than the respective CS coating. Moreover, the wear rate of the PEO-CNT coating was only 4.83 × 10−5 mm3/N·m with a relatively low coefficient of friction of 0.65, which were 59.8% and 15.6% lower than the corresponding CS coating. The corrosion current density of the PEO-treated CNT-Al coating was 3.734 × 10−6A/cm2, which was similar to the untreated CS coating. In short, the PEO treatment greatly improves the mechanical properties and wear resistance of the CS CNT-Al coating.