• Corrosion Science and Technology
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• v.22 no.6
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• pp.399-407
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• 2023

This study investigated the formation of oxide films on 6061 aluminum (Al) alloy and their impacts on corrosion resistance efficiency by regulating anodization voltage. Despite advantageous properties inherent to Al alloys, their susceptibility to corrosion remains a significant limitation. Thus, enhancing corrosion resistance through developing protective oxide films on alloy surfaces is paramount. The first anodization was performed for 6 h with an applied voltage of 30, 50, or 70 V on the 6061 Al alloy. The second anodization was performed for 0.5 h by applying 40 V after removing the existing oxide film. Resulting oxide film's shape and roughness were analyzed using field emission-scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Wettability and corrosion resistance were compared before and after a self-assembled monolayer (SAM) using an FDTS (1H, 1H, 2H, 2H-Perfluorodecyltrichlorosilane) solution. As the first anodization voltage increased, the final oxide film's thickness and pore diameter also increased, resulting in higher surface roughness. Consequently, all samples exhibited superhydrophilic behavior before coating. However, contact angle after coating increased as the first anodization voltage increased. Notably, the sample anodized at 70 V with superhydrophobic characteristics after coating demonstrated the highest corrosion resistance performance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.4
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• pp.421-428
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• 2012

In this study, the effects of surface oxide film formation on the fatigue behavior of 7075-T6 aluminum alloy were analyzed in terms of the corrosion time of the alloy. The aluminum material used is known to have high corrosion resistance due to the passivation phenomenon that prevents corrosion. Aluminum alloys have been widely used in various industrial applications such as aircraft component manufacturing because of their lighter weight and higher strength than other materials. Therefore, studies on the fatigue behavior of materials and passivation properties that prevent corrosion are required. The fatigue behavior in terms of the corrosion time was analyzed by using a four-pointing bending machine, and the surface corrosion level of the aluminum material in terms of the corrosion time was estimated by measuring the surface roughness. In addition, fractographic analysis was performed and the oxide films formed on the material surface were studied by scanning electron microscopy (SEM). The results indicated that corrosion actively progressed for four weeks during the initial corrosion phase, the fatigue life significantly decreased, and the surface roughness increased. However, after four weeks, the corrosion reaction tended to slow down due to the passivation phenomenon of the material. Therefore, on the basis of SEM analysis results, it was concluded that the growth of the surface oxide film was reduced after four weeks and then the oxide film on the material surface served as a protection layer and prevented further corrosion.

• Journal of Power System Engineering
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• v.20 no.5
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• pp.29-36
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• 2016

Aluminum alloys have been widely used in engine materials, cold & hot-water storage vessels and piping etc., Furthermore, the aluminum alloy of AC8A have been widely used in mold casting material of engine piston for various vehicles because of its properties of temperature, wear and corrosion resistance. Therefore, it is considered that evaluation of corrosion resistance as well as wear resistance of AC8A material is also important to improve its property and to prolong its lifetime. In previous paper, the effect of solution($510^{\circ}C$:4hrs) and tempering($190^{\circ}C$: 16, 24, and 36 hrs)heat treatments to corrosion resistance and hardness were investigated using electrochemical method. In this study, in order to examine completely the effect of the tempering hours to hardness variation and corrosion resistance, the results of solution($510^{\circ}C$:4hrs) and tempering($190^{\circ}C$: 2, 4, 8 and 12hrs)heat treatments to hardness and corrosion resistance were investigated using electrochemical method. The hardness decreased with solution heat treatment compared to mold casting condition, but its value increased with tempering heat treatment. Furthermore, the corrosion resistance increased with decreasing of the hardness, and decreased with increasing of the hardness reversely. And the tempering heat treatment temperature at $190^{\circ}C$ for 8 hrs exhibited the highest value of the hardness and also indicated the highest corrosion current density. However, the values of hardness and corrosion current density was again increasingly decreased with increasing of tempering hours than 8 hrs, Consequently, it is suggested that decision of the optimum. tempering hours is very important to improve the corrosion or wear resistance.

• Journal of Hydrogen and New Energy
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• v.22 no.1
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• pp.29-34
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• 2011

This study examined the effect of environmental variables, such as the NaOH concentration and solution temperature, on the rate of hydrogen generation from NaOH solutions through the corrosion of used aluminum cans as a potential candidate material for the safe and economic production of hydrogen. Corrosion of the used aluminum cans was promoted by increasing the NaOH concentration and solution temperature because of the loss of aluminum passivity. The measured rate of hydrogen generation from the NaOH solutions increased with increasing NaOH concentration due to the catalytic activity of NaOH in the hydrolysis process. However, at higher solution temperatures, the rate of hydrogen generation rate was less affected by the NaOH concentration than that at lower temperature.

• Corrosion Science and Technology
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• v.3 no.3
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• pp.102-106
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• 2004

Al foil used was 99.9 and 99.99 %. Test solution used was NaCl solution. The noise was determined using controlled potential electrolysis at -200 and -700 mV vs. NHE. The current fluctuation was caused by breakdown and repaired process of aluminum oxide film. The current fluctuation value of noise was proportion to degree of growth. The number of noise was proportion to the number of pit. The examining of current flutulation value and number of noise could be evaluated corrosion. A 99.99 % Al foil was the mostly crystal of {100} plane, and showed three-dimensional, as azimuth pit with along the direction of this place piled up. A 99.9 % Al foil was polycrystal, and in order of (311) >(222) >(200) >(111) plane. The azimuth pit did not occurred as the dissolution was occurred from each plane.

• Proceedings of the KSR Conference
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• 2002.10b
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• pp.981-986
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• 2002

ACSR of the catenary wires is corrosion degradation progressed by the effect of atmospheric pollution. ACSR which consists of galvanized steel stranded aluminum. The inside of Steel Reinforced is hot-dipped zinc coating steel wire and it takes charge of tension. If ACSR is exposed in atmosphere, the galvanic corrosion is occurred because it is contacted with aluminum. It is occurred the chemical reaction rapidly so that the local a defect is also occurred. If the catenary wires are exposed in atmosphere of pollution conditions, it may cause to reduce the mechanical strength by corrosion degradation and may cause to damage the wires by micro cracks. Accordingly, this study presents the effects of mechanical properties through the corrosion of ACSR.

• Journal of the Korean institute of surface engineering
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• v.32 no.3
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• pp.452-455
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• 1999

ORV which vaporizes LNG to NG is consisted of tube and header whose substrate is aluminum alloy. The corrosion of the tube is very severe because of sea water being used as the heating source. In this research to protect ORV substrate material, the corrosion behavior of aluminum alloys was investigated for the sacrificial role of Al-Zn alloy for ORV tubes. The electrochemical behavior of aluminum alloys in sea water was investigated. The corrosion behavior of thermally-sprayed and cladded samples were compared through salt spray tests. Al-Zn alloy can act as a sacrificial anode and cladded Al-Zn alloy has a better corrosion resistance than that of thermally sprayed one. The galvanic effect of Al-Zn to substrate material was conformed from scratched sample tests.

• Corrosion Science and Technology
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• v.8 no.3
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• pp.93-102
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• 2009

The direct-current electroetching of high purity aluminum in hot aqueous-chloride solution produces a high density of micrometer-wide tunnels whose walls are made up of the {100} planes and penetrate aluminum in the <100> directions at rates of micrometer per second. In the process of the alternating-current pitting of aluminum, cathodic polarization plays an important role in the nucleation and growth of the pits during the subsequent polarization. The direct-current tunnel etching and alternating-current etching of aluminum are basically related to the formation of poorly crystallized or amorphous passive films. If the passive film forms on the wall, a natural misfit exists between the film and the aluminum substrate, which in turn gives rise to stress in both the film and the substrate. Even though the amorphous films do not have directed properties, their stresses are influenced by the substrate orientation. The films on elastically soft substrate are likely to be less stressed and more stable than those on elastically hard substrate. The hardest and softest planes of aluminum are the {111} and {100} planes, respectively. Therefore, the films on the {111} substrates are most likely to be attacked, and those on the {100} substrates are least likely to be attacked. For the tunnel etching, it follows that the tunnel walls tend to consist of the {100} planes. Meanwhile, the tunnel tip, where active corrosion takes place, tend to be made of four closely packed {111} planes in order to minimize the surface energy, which gives rise to the <100> tunnel etching.

• Corrosion Science and Technology
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• v.12 no.1
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• pp.40-49
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• 2013

Effects of magnesium and pH on corrosion of aluminum galvanically coupled to iron have studied by using potentio- dynamic and static tests for polarization curves, Mott-Schottky test for analysis of semiconductor property, and GD-AES and XPS for film analysis. Pitting potential was sensitive to magnesium as an alloying element but not to pH, while passive current was sensitive to pH but not to magnesium. It was explained with, instead of point defect model (PDM), surface charge model describing that the ingression of chloride depends on the state of surface charge and passive film at film/solution interface is affected by pH. In addition, galvanic current of aluminum electrically coupled to iron was not affected by magnesium in pH 8.4, 0.2M citrate solution but was increased by magnesium at the solution of pH 9.1. The galvanic current at pH 9.1 increased with time at the initial stage and after the exposure of about 200 minute, decreased and stabilized. The behavior of the galvanic current was related with the concentration of magnesium at the surface. It agreed with the depletion of magnesium at the oxide surface by using glow discharge atomic emission spectroscopy (GD-AES). In addition, pitting potential of pure aluminum was reduced in neutral pH solution where chloride ion maybe are competitively adsorbed on pure aluminum. It was confirmed by the exponential decrease of pitting potential with log of [$Cl^-$] around 0.025 M of [$Cl^-$] and linear decrease of the pitting potential. From the above results, unlike magnesium, alloying elements with higher electron negativity, lowering isoelectric point (ISE), are recommended to be added to improve pitting corrosion resistance of aluminum and its alloys in neutral solutions as well as their galvanic corrosion resistance in weakly basic solutions.

• Corrosion Science and Technology
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• v.11 no.6
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• pp.280-285
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• 2012

Aluminum is on active metal, but it is well known that its oxide film plays a role as protective barrier which is comparatively stable in air and neutral aqueous solution. Thus, aluminum alloys have been widely applied in architectural trim, cold & hot-water storage vessels and piping etc., furthermore, the aluminum alloy of AC8A have been widely used in mold casting material of engine piston because of its properties of temperature and wear resistance. In recent years, the oil price is getting higher and higher, thus the using of low quality oil has been significantly increased in engines of ship and vehicle. Therefore it is considered that evaluation of corrosion resistance as well as wear resistance of AC8A material is also important to improve its property and prolong its lifetime. In this study, the effect of solution and tempering heat treatment to corrosion and wear resistance is investigated with electrochemical method and measurement of hardness. The hardness decreased with solution heat treatment compared to mold casting condition, but its value increased with tempering heat treatment and exhibited the highest value of hardness with tempering heat treatment temperature at $190^{\circ}C$ for 24hrs. Furthermore, corrosion resistance increased with decreasing of the hardness, and decreased with increasing of the hardness reversely. As a result, it is suggested that the optimum heat treatment to improve both corrosion and wear resistance is tempering heat treatment temperature at $190^{\circ}C$ for 16hrs.