Sealing as a post treatment of anodized aluminum is required to enhance the corrosion resistance by filling nanopores, which allow the penetration of corrosive media toward the base aluminum. We designed a mixed sealing solution with nickel acetate and ammonium fluoride by modifying traditional nickel fluoride cold sealing. The concentration of mixed sealing solution affected the reaction rate of sealing and corrosion current density of anodized aluminum alloy. The higher concentration of mixed sealing solution improved the sealing rate, which was represented by a decrease of corrosion current density of anodized aluminum alloy. However, a mixed sealing solution with 2/3 concentration of general nickel fluoride sealing solution operated at room temperature showed the lowest corrosion current density compared to traditional methods (e.g., nickel fluoride cold sealing (NFCS) and nickel acetate hot sealing) and other mixed sealing solutions. Moreover, the mixed sealing solution with 2/3 concentration of general NFCS had a lower risk for over sealing, which increases the corrosion current density by excessive dissolution of anodic oxide. Therefore, the mixed sealing solution with optimized conditions designed in this work possibly provides a new method for enhancing the corrosion resistance of anodized aluminum alloys.

Al-Si alloy, known for its excellent corrosion resistance and high strength, is utilized across various industries, such as electric vehicles, requiring light metal parts for efficiency. Heat treatment is an effective process for enhancing the performance of Al-Si alloys by controlling the microstructure and precipitation. Optimized heat treatment improves the mechanical properties of Al-Si alloy, including strength, hardness, and corrosion resistance. In this study, the effect of heat treatment on the microstructure, corrosion resistance, and hardness of A356 casting alloy, which has recently been used in electric vehicles, was analyzed. The as-cast A356 alloy was used as a control sample, with a solid solution treatment, followed by aging treatment. The results showed that the hardness and corrosion resistance of A356 alloy can be changed by controlling the formation and distribution of Mg₂Si precipitates within the microstructure through the solution heat treatment and following aging. Additionally, the distribution and strengthening mechanism of Mg₂Si precipitates were examined using XRD. With increasing aging time, more Mg₂Si precipitates were formed, increasing hardness. However, the precipitation of Mg₂Si reduces the corrosion resistance of A356 alloy. Thus, it was revealed that the heat treatment of A356 alloy for enhancing mechanical properties by precipitating Mg₂Si causes a side effect of corrosion resistance.

Lubricant (or oil)-impregnated porous surface has been considered as a promising surface treatment to realize multifunctionality. In this study, silicone oil was impregnated into a hard porous oxide layer created by the plasma electrolytic oxidation (PEO) of aluminum (Al) alloys. The monolayer of polydimethylsiloxane (PDMS) from silicone oil is formed on a porous oxide layer; thus, a water-repellent slippery oil-impregnated surface is realized on Al alloy, showing a low contact angle hysteresis of less than 5°. This water repellency significantly enhanced the corrosion resistance by more than four orders of magnitude compared to that of the PEO-treated Al alloy without silicone oil impregnation. The silicone oil within the porous oxide layer also provides a lubricating effect to improve wear resistance by reducing friction coefficients from ~0.6 to ~0.1. In addition, because the PDMS monolayer can be restored by frictional heat, the water-repellent surface is tolerant to physical damage to the oxide surface. Hence, the results of this fundamental study provide a new approach for the post-treatment of PEO for Al alloys.