Sealing quality critically determines the corrosion resistance of anodic oxide films on aluminum alloys. This study systematically investigated lithium nitrate-based sealing strategies, including single-step treatments at 50, 75, and 90 °C, and stepwise approaches with varying temperature gradients (50–75 °C, 50–90 °C, 50–75–90 °C). The results reveal that sealing strategies significantly impact sealing product composition and spatial distribution, thereby influencing film corrosion resistance. Low-temperature (50 °C) single-step sealing yielded boehmite and amorphous hydroxides in inner film regions, while higher temperatures (75/90 °C) promoted rapid formation of boehmite and Li–Al-LDH (lithium–aluminum layered double hydroxide) in outer regions. Stepwise sealing combines deep low-temperature penetration with high-temperature Li–Al-LDH formation kinetics, creating gradient composite structures that enhance film compactness and stress relief. Electrochemical and salt spray tests demonstrated that 50–75 °C stepwise-sealed samples exhibited the lowest corrosion current density and highest impedance, with superior performance in both neutral (pH 7.0) and acidic (pH 3.5) environments. This work elucidates lithium salt sealing mechanisms through temperature control and provides guidelines for eco-friendly, high-performance aluminum surface treatments.
Li et al. (Mon,) studied this question.