• Corrosion Science and Technology
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• v.16 no.5
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• pp.241-246
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• 2017

The comparative results of corrosion testing in humid tropical atmosphere in rural and coastal areas for hot dipped zinc coatings are presented below. The test was conducted in outdoor conditions over a period of five years. The mass loss and other performance characteristics of two types of zinc coatings were evaluated, analysed and discussed in relation to the climatic and environmental parameters. The corrosion rates of the coatings exposed to coastal conditions were about three times higher than the corrosion rates appreciated in rural conditions. The data demonstrates that the corrosion process obeys an equation of the form $M=At^n$, where M is the loss of metal and t is the time of exposure. A and n are constants which values depend on the environmental characteristics and the physicochemical behavior of the corrosion products respectively. Corrosion is strongly influenced by atmospheric time of wetness (TOW) and airborne salinity. The nature and composition of corrosion products are also considered. Simonkolleite, a major crystalline phase, was found in the zinc corrosion products exposed to coastal conditions, while zinc hydroxide and zinc hydrosulfate are easily found in rural settings.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.10
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• pp.4653-4657
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• 2013

The atmospheric corrosion rate were measured in Asan area for four years according to ISO 9224. The tested metals chosen as the most frequently used in industry, aluminum were copper, carbon steel, weathgering steel, and galvanized steel. The assessed corrosivity categories was 3 in average. The corrosivity categories of asan area was higher than typical rural area and even urban area, whereas it slightly lower than marine area. The results were discussed, specially as the regional climatic characteristics.

• Corrosion Science and Technology
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• v.3 no.2
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• pp.47-53
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• 2004

The conditions to simulate the atmospheric corrosion behavior in the laboratory were investigated to clarify atmospheric corrosion mechanism of steel material in coastal area, For airborne sea salt and artificial seawater droplet, the various behaviors were observed by optical microscope, The particle size of the dried airborne sea salt was about $20{\mu}m$, and was about 1/10 compared with the artificial seawater droplet. Though the airborne sea salt represented the same behavior as the thermodynamic water absorption, the behavior of the artificial seawater droplet deviated from the results of the thermodynamic calculation, It is concluded that the water absorption behavior is influenced by the particle size of the dried sea salt. The corrosion behaviors of carbon steels were observed under the deposited condition of airborne sea salt and artificial seawater droplet. The corrosion behaviors showed a different trend, indicating that the corrosion behavior depended on the particle size of the dried sea salt. The corrosion in the actual environrnent progressed greater than that in the chamber. Furthermore, the summer showed the greater corrosion than the spring. It is found that the corrosion behaviors are attributed to the influence of the environmental factors.

• Journal of the Korean institute of surface engineering
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• v.52 no.2
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• pp.62-71
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• 2019

Al1050 and Al7075 alloy specimens were exposed to atmospheric conditions for 24 months and analyzed by Transmission Electron Microscopy to characterize their corrosion behavior and oxide film characteristics, especially focusing on intergranular corrosion or oxidation. In general, the intergranular oxygen penetration depth of Al1050 was deeper than Al7075. Since O and Si signals were overlapped at the oxidized grain boundaries of Al1050 and Mg is not included in Al1050, it is concluded that Si segregated along the grain boundaries directly impacts on the intergranular corrosion of Al1050. Cr-Si or Mg-Si intermetallic particles were not observed along the grain boundaries of Al7050, but Mg-Si particle was barely observed in the matrix. 10-nm size Mg-Zn particles were also found all over the matrix. Mg was mainly observed along the oxidized grain boundary of Al7075, but Si was not detected due to the Mg-Si particle formation in the matrix and relatively low concentration of Si in Al7075. Therefore, it is thought that Mg plays an important role in the intergranular corrosion of Al7075 under atmospheric corrosion conditions.

• Journal of the Korean Society for Railway
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• v.12 no.5
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• pp.725-731
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• 2009

For structural design and diagnosis, quantitative relationship between corrosive degradation and variation of mechanical properties such as tensile strength and fatigue strength is needed. But it is difficult to find experimental data associated with corrosive degradation of structural structures in the literature. In this study, first of all I established the atmospheric corrosion test procedure. And using specimens of SM490A and SS400 on the atmospheric corrosion test bed, I carried out tensile and fatigue tests at regular intervals. And we studied the effect of post-weld heat treatment on the tensile and fatigue behaviour. It is found fatigue strength decreases as the atmospheric corrosion period increases.

• Corrosion Science and Technology
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• v.17 no.1
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• pp.6-11
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• 2018

Outdoor exposure tests using of 7B04 aluminium alloy samples including plate, tensile and various SCC samples were carried out in Tuandao station, Shandong province (East of China) and Wanning station, Hainan province (South of China). Corrosion characteristics including weight loss, microstructure, tensile strength and SCC susceptibility were investigated. The corrosion rates in Tuandao and Wanning showed high to low and the corrosion rates changed to the following equation of $w=at^b$ (b<1). The corrosion of 7B04 aluminium alloy in Wanning was more serious than that in Tuandao. Pitting appeared at early stage of expose test, and it can be changed to general corrosion with test time extension. The 7B04 aluminium alloy of which specimen shapes are forging and thick plate also showed SCC (Stress corrosion cracking) in the marine atmosphere. The higher SCC sensitivity was observed in Wanning station than in Tuandao station. The 7B04 aluminium alloy with a high stress level was more sensitive to SCC. Intergranular and transgranular or a mixed mode of cracking can be observed in different marine exposure.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1998.05a
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• pp.3-3
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• 1998

The atmospheric corrosIOn properties of Zinc (Zn) under wet/dry transition of $H_20$ film were investigated in this study. The atmospheric corrosion of metal is usually occurred as a result of repetitious thickness transition (so called wet/dry transition) of liquid phase which is covering the metal surface. Corrosion potential and the polarization behaviour of Zn during liquid film thickness transition were measured by Kelvin probe method which IS using vibrating reference electrode without touching the liquid film. The oxidized states of Zn as a result of successive wet/dry transition were also investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that the corrosion potential and the corrosIOn rate of Zn both are increasing during drying. However, the corrOSIon rate is decreasing again when the Zn surface is completely dried while the corrosion potential still remains high. This behaviour can be explained by the polarization behaviour change of Zn according to the $H_20$ film thickness change. The completely dried surface is consisted mostly with Zn and ZnO phases. After a number of cycles of wet/dry transition, however, the oxidized Zn phase of ${\varepsilon}-Zn(OH)_2$, which has rather voluminous and defected structure, were found.

• Journal of the Korean institute of surface engineering
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• v.54 no.2
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• pp.62-70
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• 2021

Al2024 aluminum alloy specimens were exposed to atmospheric conditions for maximum 24 months and analyzed by electron microscopes to characterize their corrosion behavior and oxide film characteristics. As the exposure time increased from 12 months to 24 months, the number of pitting sites per 1 mm² increased from ~100 to ~200. The uniform oxidation (or non-pitting) region of the 12-month exposure specimen showed 30~120 nm thick oxide layer, whereas the 24-month exposure specimen showed 170~200 nm thick oxide with the local oxygen penetration region up to 1 ㎛ deep. There was no local corrosion area observed in the 12-month exposure specimen except pitting. However, in the 24-month exposure specimen, local oxygen penetration region was observed beneath the uniform oxide layer and near the pitting cavity. Al2024 showed two times thicker uniform oxide layer but much shallower local oxygen penetration region than Al1050, which appears to be related to low Si concentration. Further research is needed on the effects of Mg segregation near the tip of the oxygen penetration region.

• Corrosion Science and Technology
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• v.2 no.4
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• pp.165-170
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• 2003

Atmospheric corrosion behaviors of Zn, Zn-5%Al and Zn-55%A l coated steels have been investigated under cyclic wet-dry environments containing chloride ions. The wet-dry cycle was carried out by alternate exposure to immersion in 0.5 M (or 0.05 M) NaCl solutions and drying at $25^{\circ}C$ and 60 %RH. The polarization resistance $R_p$ and solution resistance $R_s$ were monitored by AC impedance technique. From the obtained $1/R_p$ and $1/R_s$ values, the corrosion rate of the coatings and the Time of Wetness (TOW) were estimated, respectively. Effects of chloride ions and TOW on the corrosion rates of Zn, Zn-5%Al, Zn-55%Al coatings and appearance of red rust (onset of underlying steel corrosion) under wet-dry cycles are discussed on the basis of the corrosion monitoring data.

• Corrosion Science and Technology
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• v.7 no.6
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• pp.324-327
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• 2008

Stainless steels have been widely used as a building exterior materials in Asian countries for the last decade. It is required for the materials in this field to have an aesthetic appearance, a relatively high strength, and an excellent corrosion resistance. Other metallic materials such as copper, aluminum, and carbon steels have been also used as the exterior materials. Considering the cost of maintenance, stainless steel, having the outstanding corrosion resistance, is replacing other materials in the several parts in the building exteriors. Ferritic stainless steel has been applied as the roofing materials because its thermal expansion is much smaller than that of austenitic stainless steel. Therefore, it is suitable for the large-scale construction such as airport terminal, convention center, and football stadium. To improve the corrosion resistance of the ferritic stainless steels, the modification of alloy composition has been studied to develop new grade materials and the progress in the surface technology has been introduced. Corrosion properties of these materials were evaluated in the laboratory and in the field for longer than two years. High-Cr ferritic stainless steel showed excellent corrosion resistance to the atmospheric environments. In the region close to the sea, the corrosion resistance of high-Cr ferritic stainless steel was much superior to that of other materials, which may prove this steel to be the appropriate materials for the construction around seashore. In some of the large constructions around seashore in South Korea, high-Cr ferritic stainless steels have been used as the building exterior materials for six years.