• Bulletin of the Korean Chemical Society
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• v.24 no.7
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• pp.975-980
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• 2003

The electrochemical properties and the mechanism of formation of anodic oxide films on Mg alloys containing 0-15 mass% Al, when anodized in NaOH solution, were investigated by focusing on the effects of anodizing potential, Al content, and anodizing time. The intensity ratio of Mg(OH)₂ in the XRD analysis decreased with increasing applied potential, while that of MgO increased. Mg(OH)₂ was barely detected at 80 V, while MgO was readily detected. The anti-corrosion properties of anodized specimens at each constant potential were better than those of non-anodized specimens. The specimen anodized at an applied potential of 3 V had the best anti-corrosion property. The intensity ratio of the β phase increased with aluminum content in Mg-Al alloys. During anodizing, the active dissolution reaction occurred preferentially in β phase until about 4 min, and then the current density increased gradually until 7 min. The dissolution reaction progressed in α phase, which had a lower Al content. In the anodic polarization test in 0.017 mol·$dm^{-3}$ NaCl and 0.1 mol·$dm^{-3}$ Na₂SO₄ at 298 K, the current density of Mg-15 mass% Al alloy anodized for 10 min increased, since the anodic film that forms on the α phase is a non-compacted film. The anodic film on the α phase at 30 min was a compact film as compared with that at 10 min.

• Journal of the Korean institute of surface engineering
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• v.53 no.1
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• pp.15-21
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• 2020

In this study, growth and burning behavior of 6061 aluminum alloy was studied under constant anodic voltages at various temperatures and magnetic stirring rates in 20% sulfuric acid solution by analysing I-t curves, measuring thickness and hardness of aluminum anodic oxide (AAO) films, observations of surface and cross-sectional images of AAO films. AAO films were grown continuously at lower voltages than 18.5V but burning occurred when a voltage more than 19V was applied in 20% H₂SO₄ solution at 20±0.5℃ and 200 rpm of magnetic stirring. The burning was always related with an extremely large increase of anodic current density with anodizing time, suggesting that high heat generation during anodizing causes deteriorations of AAO films by chemical reaction with acidic solutions. The burning resulted in decreases of film thickness and hardness, surface color brightened and formation of porous defects in the AAO films. The burning voltage was found to decrease with increasing solution temperature and decreasing magnetic stirring rate. The decreased burning voltages seem to be closely related with increased chemical reactions between AAO films and hydrogen ions.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.7
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• pp.14-21
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• 2019

Large-diameter hydraulic devices such as the hydraulic reservoir in aircraft that serves to balance the hydraulic pressure in the various hydraulic devices in the cabin and to store hydraulic oil are operated by the internal piston systems. However, since this operates in an environment with high temperature and humidity, it may cause the inner surface to flake during its operation. Therefore, an anodizing surface treatment is applied to improve the corrosion resistance, abrasion resistance, and smooth operation. However, anodizing increases the surface roughness. Accordingly, the polishing process that improves the surface roughness after anodizing is important. However, the existing polishing process is performed manually, which results in an inefficient process. Therefore, in this study, we selected the optimum polishing conditions for effective polishing using the experimental design to improve the polishing process for the $Al_2O_3$ film that forms after anodization. Through experiments, we confirmed that the surface uniformity after polishing was superior as the feed rate was slower when the same polishing time had been applied.

• Corrosion Science and Technology
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• v.22 no.4
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• pp.221-231
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• 2023

Interest in aluminum alloys for the hydrogen valves of fuel cell electric vehicles (FCEVs) is growing due to the reduction in fuel efficiency by the high weight. However, when an aluminum alloy is used, deterioration in mechanical characteristics caused by hydrogen embrittlement and wear is regarded as a problem. In this investigation, the aluminum alloy used to prevent hydrogen embrittlement was subjected to surface treatments by performing hard anodizing and plasma ion nitriding processes. The hard anodized Al alloy exhibited brittleness in which the mechanical characteristics rapidly deteriorated due to porosity and defects of surface, resulting in a decrease in the ultimate tensile strength and modulus of toughness by 15.58 and 42.51%, respectively, as the hydrogen charging time increased from 0 to 96 hours. In contrast, no distinct nitriding layer in the plasma ion-nitrided Al alloy was observed due to oxide film formation and processing conditions. However, compared to 0 and 96 hours of hydrogen charging time, the ultimate tensile strength and modulus of toughness decreased by 7.54 and 13.32%, respectively, presenting excellent resistance to hydrogen embrittlement.

• Journal of the Korean institute of surface engineering
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• v.51 no.2
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• pp.87-94
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• 2018

Various sealing techniques were applied to the anodized 5083 aluminum alloy for marine environment to reduce corrosion and cavitation erosion damage. Electrochemical experiments and cavitation erosion tests were conducted to evaluate the corrosion resistance and cavitation resistance of the anodic oxide film treated with sealing in natural seawater solution. Then, damaged surface morphology was analyzed by scanning electron microscope(SEM) and 3D microscope. As the results of the electrochemical experiments, it was observed that the surface damage of all the experimental conditions in the anodic polarization experiment was locally grown by the combination of crack and corrosion damage. In the Tafel analysis, the corrosion resistance of all sealing treatment conditions was improved compared to the anodizing. On the other hand, cavitation erosion tests showed that the anodizing and all the sealing treatment conditions generated local pit damage by cavitation erosion attack and grew to crater damage in the observation of damaged surface by SEM. Also, the weight loss and the surface damage depth measured with the experiment time presented that most of the sealing treatment conditions showed better cavitation erosion resistance than the anodizing, and they had an incubation period at the beginning of the experiment.

• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.463-466
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• 2011

In this work, we investigate anodization of Pb in ethylene glycol containing small amount of $NH_4F$, demonstrating that ${\beta}-PbF_2$ particles with octahedral morphology can be prepared by adjusting the applied potential and anodizing time. FE-SEM images and XRD measurements of anodic nanostructures as a function of anodizing time clearly show that PbO is first formed on Pb. Subsequently, a local dissolution of PbO leads to formation of skeleton structure of PbO, releasing $Pb^{2+}$ ions in the electrolyte. The lead ions can be precipitated on the walls or intersection of the skeleton walls when the concentration of lead ions is saturated. The method described in this article shows the feasibility of formation of metal fluoride crystal by anodization of metal in a fluoride containing solution.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.52-52
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• 2003

• Corrosion Science and Technology
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• v.21 no.4
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• pp.282-289
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• 2022

Aluminum 1000 series alloy, a pure aluminum with excellent workability and weldability, is mainly used in the ship field. Aluminum alloy can combine with oxygen in the atmosphere and form a natural oxide film with high corrosion resistance. However, its corrosion resistance and durability are decreased when it is exposed to a harsh environment for a long period of time. For solving this problem, a porous oxide film can be formed on the surface using an anodizing treatment method, a typical surface technique among various methods. In this study, aluminum 1050 alloy was anodized for 2 minutes, 6 minutes, and 10 minutes. The structure and shape of the oxide film were then analyzed to determine the corrosion resistance according to the thickness of the oxide film that changed depending on working condition using 15 wt% NaCl. After it was immersed in NaCl solution for 1, 5, and 10 days, corrosion damage was observed. Results confirmed that the thickness of the oxide film increased as the anodization time became longer. The depth of surface damage due to corrosion became deeper when the film was immersed in the 15 wt% NaCl solution for a longer period of time.

• Journal of the Korean institute of surface engineering
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• v.43 no.4
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• pp.180-186
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• 2010

$TiO_2$ nanotubes were formed on Ti by anodizing in 1 M $H_3PO_4$ + 0.3 M HF and 0.1 M $NH_4F$ + 2% $H_2O$ in ethylene glycol, and their surface and cross-sectional morphologies were observed using FE-SEM as a function of anodizing time and applied voltage. The cross-section of the $TiO_2$ nanotubes was readily observed from the small pieces of nanotubes remaining near the scratch lines after scratching of the anodized surface. $TiO_2$ nanotubes was observed to grow faster and thicker in non-aqueous solution than in aqueous solution. Diameter of $TiO_2$ nanotubes was proportional to the applied voltage, irrespective of the type of the electrolyte, and it is recommended to use non-aqueous solutions for the preparation of larger diameter of $TiO_2$ nanotubes.

• Journal of the Korean institute of surface engineering
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• v.57 no.3
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• pp.201-207
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• 2024

This study compared the chemical resistance properties according to various sealing treatment methods for the anode film formed during the anodization process of Al6061 alloy. Al6061 aluminum was used in four different sealing treatment methods: boiling water sealing, lithium sealing, nickel sealing, and pressurized sealing, and each sample was evaluated for corrosion resistance through a 5% HCl bubble test and the microstructure was observed through a scanning electron microscope(SEM). According to the results, corrosion resistance increased as time and temperature increased in all sealing treatment methods. Relatively, corrosion resistance was high in the order of boiling water sealing, lithium sealing, nickel sealing, and pressure sealing, and the best corrosion resistance was found in pressure sealing. These research results can be helpful in selecting a process necessary to improve the efficiency and performance of anodizing process in the industrial field using aluminum alloys.