Effect of oxidation time on the microstructure, mechanical properties, and corrosion resistance of MAO ceramic film on 5B70 Al alloy

• Systematically revealed the time-dependent evolution of the MAO coating structure. • First proposal of an “optimal oxidation time window” for constructing high-quality MAO ceramic film. • Coupled multi-source characterization reveals elemental participation mechanism. • Revealing the correlation mechanism between micro-defects and discharge behavior. A ceramic film on 5B70 Al alloy was prepared using the MAO technique in an alkaline sodium metasilicate electrolyte. The effect of oxidation time on the microstructure, the ceramic/metal interface structure, and corrosion resistance was systematically investigated. The results showed that with the increase of oxidation time, the film thickness gradually increased, while the surface porosity and roughness significantly decreased. The density and uniformity of the ceramic film improved. The amount of Al 3 Sc nanoparticles precipitated increased, and their distribution became more uniform, causing the grain of the ceramic film to gradually refine, thereby significantly enhancing its corrosion resistance. The MAO ceramic film prepared with an oxidation time of 15 min exhibited the best corrosion resistance. However, when the oxidation time exceeded 15 min, the MAO ceramic film became too thick, and defects such as voids and cracks appeared at the ceramic/metal interface, leading to the intensification of localized corrosion. This study optimized the MAO process, offering valuable guidance for improving protective performance of Al alloys in corrosive environments, particularly in aerospace and nuclear power.