Purpose The purpose of this paper is to investigate the effect of Na2SiO3 concentration on the microstructure and corrosive properties of microarc oxidation (MAO) coating on Al-Mg-Sc alloy and explore microstructure evolution rule of Al substrate in the contact area. Design/methodology/approach The Na2SiO3 concentration in electrolytes influenced the microstructure and corrosion behavior of MAO coatings. Instantaneous high temperature and high pressure due to microarc discharge caused annealing treatment. The corrosive behavior of the MAO coating was featured with polarization curves and electrochemical impedance spectrum in 3.5 Wt.% NaCl solution. Findings The substrate in the contact area existed the instantaneous annealing treatment, which caused obvious recrystallization. The coating prepared in electrolyte containing 7 g/L Na2SiO3 exhibited the highest protective properties in 3.5 Wt.% NaCl solution. Originality/value MAO treatment could increase the corrosion resistance by producing a protective layer on the Al-Mg-Sc alloy surface at a suitable Na2SiO3 concentration and microstructure evolution rule of Al substrate in the contact area was obtained.

Although Al-Mg-Sc alloy was widely applied to aviation aerospace field, they were vulnerable to local corrosion and wear in the process of long-term service in severe environmental conditions. In this paper, micro-arc oxidation (MAO) ceramic films on Al-Mg-Sc alloy substrate were prepared in electrolyte solutions with different Na 2 SiO 3 concentrations, and the corrosion resistance and wear resistance of the MAO samples were studied. The experimental results of potentiodynamic polarization (PDS) and long-term immersion tests indicated that the MAO ceramic film prepared in 10 g/L Na 2 SiO 3 electrolyte solution had the best corrosion resistance, as manifested by no obvious cracks, serious collapse and corrosion products on the sample surface and no deep cracks and corrosion paths in the cross-sectional area. The increase of Na 2 SiO 3 concentration in electrolyte solution also improved the wear resistance of MAO ceramic film, as manifested by low wear depth (10 μm)and width (1 mm) of the MAO ceramic film prepared in 10 g/L Na 2 SiO 3 electrolyte solution against GCr15 steel ball. Studies in mechanisms suggested that as the Na 2 SiO 3 concentration in the electrolyte increased, the MAO ceramic film became denser, which could prevent the penetration of corrosive medium, promote the generation of the anti-wear layer with SiO 2 as the main component to enhance the wear resistance. MAO ceramic film formed in Na 2 SiO 3 electrolyte solution provided good protective performance for Al-Mg-Sc alloy in the corrosion and wear conditions, which had a broader application prospect.

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Hard and wear-resistant ceramic coatings with SiC nanoparticles were in situ fabricated on Al-Mg-Sc alloy using micro-arc oxidation (MAO) method in alkaline silicate electrolyte. The microstructure, roughness, and composition of the MAO coatings were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD) and laser scanning confocal microscopy (LSCM), respectively. The microhardness of the MAO coatings was obtained microhardness tester. The wear resistance of the MAO coatings was evaluated by ball-on-disc reciprocating tribo-tester. The results showed that the phase composition of the obtained coatings with the typical pancake-like stacking structures was mainly composed of α-Al 2 O 3 and γ-Al 2 O 3 . the porosity and roughness gradually decreased with the increment of SiC nanoparticles concentration. Al content gradually decreased from the matrix to the outside, while the Si content gradually increased. The incorporation of SiC nanoparticles further increased the microhardness of the MAO coating. Especially in alkaline silicate electrolyte with 1.5g l −1 SiC nanoparticles, the microhardness could reach 1270 HV 0.5 . The friction coefficient of the MAO coatings prepared in electrolyte solution with SiC addition varied from 0.4 to 0.55, and the ceramic coating with 1.5g l −1 SiC nanoparticles exhibited the best wear resistance. The wear mechanism was attributed to be the combination of abrasive wear, adhesive wear and oxidation wear.

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