• Journal of Surface Science and 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.

• Computers and Concrete
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• v.27 no.5
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• pp.437-445
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• 2021

Retrofitting of structures has gained importance over the recent years. Particularly, Reinforced Cement Concrete (RCC) column strengthening has become a challenge to the structural engineers, owing to the risks and complexities involved in it. There are several methods of RCC column strengthening viz. RCC jacketing, steel jacketing and Fiber Reinforced Polymer (FRP) wrapping etc., FRP wrapping is the most promising alternative when compared to the others. The large research database shows FRP wrapping, through lateral confinement, improves the axial load carrying capacity of the columns under concentric loading. However, its confining efficiency reduces under eccentric loading. Hence a relative newer technique called Near Surface Mounting (NSM), in which Carbon FRP (CFRP) strips are epoxy grouted to the precut grooves in the cover concrete of the columns, has been thrust domain of research. NSM technique strengthens the column nominally under concentric load case while significantly under eccentric case. A novel configuration of NSM in which the vertical NSM (VNSM) strips are being connected by horizontal NSM (HNSM) strips was numerically investigated under both concentric and eccentric loading. It was found that the configuration with 6 HNSM strips performed better under eccentric loading than under concentric loading, while the configuration with 3 HNSM strips performed better under concentric loading than under eccentric loading. Hence an optimum of 4 HNSM strips is recommended as strengthening measure for the given column specifications. It was also found that Aluminum alloy cannot be used instead of CFRP in NSM applications owing to its lower mechanical properties.

• Journal of Surface Science and Engineering
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• v.17 no.2
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• pp.29-40
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• 1984

The structure of rapidly solidified Al-Si-based alloys and its relationship to subsequent anodic film growth in near neutral and acid solutions have been investigated. Solidification of the alloys proceeds via pre-dendritic nuclei, associated with rugosity of the casting surface, from which cellular-type growth, comprised of aluminium-rich material surrounded by silicon-containing material, emanates. Observation of ultramicrotomed sections of the alloys and their anodic films reveals the local oxidation of the silicon-rich phase and its incorporation into the anodic alumina film, formed in near neutral solutions. Such incorporation occurs but resultant isolation of the silicon-rich phase is not possible for anodizing in phosphoric acid, and a three-dimensional network of the oxidized silicon-containing phase, with continuing development of porous anodic alumina, is observed.

• Journal of Magnetics
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• v.17 no.3
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• pp.185-189
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• 2012

The coercivity of near single domain size $Nd_2Fe_{14}B$-type particles prepared by ball milling of HDDR-treated $Nd_{12.5}Fe_{80.6}B_{6.4}Ga_{0.3}Nb_{0.2}$ alloy was investigated. The feasibility of a surface nitrogenation for improving the coercivity stability of the fine $Nd_2Fe_{14}B$-type particles was also studied. The near single domain size $Nd_2Fe_{14}B$-type particles had a high coercivity of over 9 kOe. However, the coercivity radically deteriorated as the temperature increased in air (< 2 kOe at $200^{\circ}C$). This coercivity reduction was attributed to the soft magnetic phases, ${\alpha}$-Fe and $Fe_3B$, which formed on the surface of the fine particle due to oxidation. Surface nitrogenation of the fine particles significantly improved the stability of their coercivity. The improvement in coercivity stability was attributed to the formation of a thin nitrogenated layer on the surface of the fine $Nd_2Fe_{14}B$-type particles, which enhanced the anisotropy field and gave improved resistance to oxidation (dissociation).

• New & Renewable Energy
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• v.2 no.4 s.8
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• pp.64-69
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• 2006

There is a worldwide interest in the development and commercialization of polymer electrolyte membrane fuel cells [PEMFCs] for vehicular and stationary applications. One of the major objectives is the reduction of loaded electrode materials, which is comprise of the Pt-based noble metals. In this paper, a novel chemical strategy is described for the preparation and characterization of carbon-supported and surface-alloys, which were prepared by using a successive reduction process. After preparing Au colloid nanoparticles, the supporting of Au colloid nanoparticles occurred spontaneously in the carbon black-dispersed aqueous solution. Then nano-scaled active materials were formed on the surface of carbon-supported Au nanoparticles. The structural and electrochemical analyses indicate that the active materials were deposited on the surface of Au nanoparticles selectively and that an alloying process occurred during the successive reducing process. The carbon-supported & surface-alloys showed the higher electrocatalytic activity than those of the particle-alloys and commercial one [Johnson-Matthey] for the reaction of methanol and formic acid oxidation. The increased electrocatalytic activity might be attributed to the effective surface structure of surface-alloys, which have a high utilization of active materials for the surface reaction of electrode.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.584-595
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• 1991

In the direct rolling processes for the mushy state alloy, a mushy state material which simultaneously contains liquid-solid phase is obtained from the exit port of stirring apparatus with a given solid fraction. This solid fraction is dependent on the temperature of within the solid-liquid range which shows to be controlled accurately by the experimental conditions for a given stirring apparatus. Rolling conditions for fabrication the fine surface strip were obtained from direct rolling experiment with mushy state alloys of Sn-75%Pb and aluminum alloy. Influence of solid fraction, rolling speed and initial roller gap on the state of strip surface and solidified structure was observed. We proposed theoretical model for prediction of rolling force, and we compared calculation result and experimental value measured with load cell.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05c
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• pp.213-218
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• 1996

Characteristics of high density U-Mo alloy powder prepared by centrifugal atomization have been examined. The results indicate that the majority of the atomized U-Mo alloy particles has a smooth surface and frequently near-perfect spheroidal shape with few satellites attached. The size distribution of atomized U-Mo alloy powder shows the mono-modal size distribution seen in ligament disintegration mechanism. All phases of atomized alloy powder below 150$\mu\textrm{m}$ irrespectively to particle size are found to be ${\gamma}$-U (cubic structure) phases with isotropic structure and not to be U$_2$Mo phase at all. The microstructure of atomized U-Mo alloy particulates has micro-crystalline structure with non-dendritic gram supersaturated with Mo element. Also the grain size of ${\gamma}$ -U tends to decrease with the decrease of the powder diameter.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.534-538
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• 2002

Dissimilar friction stir welding of aluminum (AI) alloy 1050 and magnesium (Mg) alloy AZ31 was successfully done in the limited welding parameters. The dissimilar weld showed good quality and facility compared to conventional fusion weld. Transverse cross section perpendicular to the welding direction had no defects. The weld was divided into base material of Al alloy, an irregular shaped stir zone and base material of Mg alloy. The irregular shaped stir zone was roughly located around the initial weld center. The weld interface near plate surface shifted from initial weld centerline to the advancing side. Hardness profile of the weld was heterogeneous, and the hardness value of the stir zone was raised to about 150 Hv to 250 Hv. The mixed phase was identified to intermetallic compound $Mg_{17}$Al$_{12}$ using x-ray diffraction method, energy dispersive x-ray spectroscopy (EDX) and electron probe micro analysis (EPMA). The formation of intermetallic compound $Mg_{17}$Al$_{12}$ during FSW causes the remarkable increase in hardness value in the stir zone.one.

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.2
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• pp.41-53
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• 1994

In this paper, rotating-bending fatigue tests of the SiC-whisker- reinforced 6061-T6 aluminum alloy and 6061-T6 alumiunm alloy made by power metallurgy were carried out to investigate the fatigue characteristics of plain and notched specimens at room temperature. The fatigue mechnisms in both materials were clarified through successive surface observations using the plastic replica method. In the case of the SiC-whisker-reinforced composites, there are whisker rich and poor zones and the fatigue crack is nucleated from the end of whiskers near the boundary. On the other hand, in the case of the 6061-T6 aluminum alloy, the fatigue crack is nucleated from defects and propagates by shear. Moreover, the results were discussed based on linear notch mechanics.

• International Journal of Precision Engineering and Manufacturing
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• v.4 no.4
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• pp.45-50
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• 2003

In order to investigate the effect of surface treatment (Anodizing) and rolling on AI 5083-H131 alloy, under hyper velocity impact, a ballistic testing was conducted. Ballistic resistance of these materials was measured by a protection ballistic limit ($V_{50}$)' a statistical velocity with 50% probability of penetration. Perforation behavior and ballistic tolerance, described by penetration modes, were respectfully observed, by $V_{50}$ test and Projectile Through Plates (PTP) test at velocities greater than $V_{50}$. PTP tests were conducted with 0$^{\circ}$ obliquity at room temperature using 5.56mm ball projectiles. $V_{50}$ tests with 0$^{\circ}$ obliquity were also done with projectiles that were able to achieve near or complete penetration during PTP tests. Resistance to penetration, and penetration modes of Al 5052-H34 alloy were compared to those of Al 5083-H 131 alloy.