• Journal of Korea Foundry Society
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• v.31 no.6
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• pp.342-346
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• 2011

A328 alloy is an attractive candidate for recycle-friendly aluminum alloy in the recycling of automotive components. In this study, A328 alloy melt was degassed by ultrasonic vibration and the effect of treatment time on the density, fluidity and mechanical properties was investigated. Experimental results reveal that a constant value of density can be reached after less than 180 seconds of ultrasonic treatment time, but the density decreased when the treatment time was 300 seconds. Ti which was dissolved from the horn during ultrasonic treatment reduced the fluidity of melt. After degassing by ultrasonic vibration for 180 seconds, tensile strength increased from 201MPa to 250MPa, and elongation increased from 2.38% to 3.50%, however, further treatment deteriorated the mechanical properties.

• Korean Journal of Materials Research
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• v.29 no.5
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• pp.328-335
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• 2019

Nb-doped $TiO_2$(NTO) coated NiCrAl alloy foam for hydrogen production is prepared using ultrasonic spray pyrolysis deposition(USPD) method. To optimize the size and distribution of NTO particles based on good physical and chemical stability, we synthesize particles by adjusting the weight ratio of the Nb precursor solution(5 wt%, 10 wt% and 15 wt%). The morphological, chemical bonding, and structural properties of the NTO coated NiCrAl alloy foam are investigated by X-ray diffraction(XRD), X-ray photo-electron spectroscopy(XPS), and Field-Emission Scanning Electron Microscopy(FESEM). As a result, the samples of controlled Nb weight ratio exhibit a common diffraction pattern at ${\sim}25.3^{\circ}$, corresponding to the(101) plane, and have chemical bonding(O-Nb=O) at 534 eV. The NTO particles with the optimum weight ratio of N (10 wt%) show a uniform distribution with a size of ~18.2-21.0 nm. In addition, they exhibit the highest corrosion resistance even in the electrochemical stability estimation. As a result, the introduction of NTO coated NiCrAl alloy foam by USPD improves the chemical stability of the NiCrAl alloy foam by protecting the direct electrochemical reaction between the foam and the electrolyte. Thus, the optimized NTO coating can be proposed for excellent protection of NiCrAl alloy foam for hydrocarbon-based steam methane reforming(SMR).

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.328-329
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• 2007

A study on the texture and the formability after frictional rolled and subsequent heat-treated AA 1050 aluminum alloy sheets have been carried out. The specimens after the frictional rolling showed a very fine grain size, a decrease of <100>//ND, and an increase of <111>//ND textures. The change of plastic strain ratios has been investigated and it was found that they were higher than those of the initial Al sheet.

• Proceedings of the KWS Conference
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• 2007.11a
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• pp.328-331
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• 2007

It was carried out to evaluate microstructure and mechanical properties of friction stir welded(FSW) on magnesium alloys. Two types magnesium alloy was used in this work, AZ31 wrought and AZ91 cast magnesium alloy. Microstructure near the weld zone showed general weld structures such as stir zone(SZ), thermo-mechanically affected zone(TMAZ) and heat affected zone(HAZ). In the AZ91 alloy, the SZ had a fine grain size and $\beta$ phase particles which were well distributed in matrix. It was characterized to redistribute by partial or full re-solution of the $\beta$ phase which is coarse in base metal during FSW processing. The hardness of the SZ slightly increase than the base metal in AZ31 Mg alloy.

• Journal of Korea Foundry Society
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• v.21 no.6
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• pp.328-335
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• 2001

The objective of this study is to investigate on manufacturing Al-scrap into hypereutectic Al-Si alloy by using electromagnetic force. The Fe element in the aluminium scrap was controlled by intermetallic compound method and using EMF(electromagnetic force). The most lumped compound was found after 10min holding at $690^{\circ}C$. A number of segregated compound was revealed when imposed to EMF at 30A. The refinement of primary Si particles was achieved by EMF stirring. Primary Si particles were refined and spheroidized most of all with the magnetic intensity of 180G for 10 min.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.4
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• pp.328-338
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• 2007

One of main advantages of composite using smart material as reinforcement can be controlled cracks behavior inside the composite. If the smart composite is applied as part of the structure, the use of the shape memory effect of the smart material is the best way to protect the propagation of cracks generated in the structure while use. In this study, the optical manufacturing conditions for the smart composite were derived. In order to evaluate the shape memory effect by shape memory alloy, the tensile load was applied to the smart composite and stress distribution was inspected. And then, the smart composite was heated to a certain temperature and the shape memory alloy would shrink to the original shape. Finally, at this point the recovering status of stress using photoelastic instrument was discussed.

• Transactions of Materials Processing
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• v.6 no.4
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• pp.319-328
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• 1997

A flow stress involving strain, solid fraction, and breakage ratio, and solid fraction updating algorithm were proposed to depict the deformation behavior of materials at the semi-solid state. In case of isothermally simple upsetting of Sn-15%Pb alloy at the semi-solid state, by comparing the results of finite element analysis with the existing experimental results, the reliability of both the developed flow stress and updating algorithm were investigated. It was found that the verified program can effectively be used in the rigid-viscoplastic finite element analysis of the semi-solid forging processes.

• Journal of the Korean Society for Heat Treatment
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• v.16 no.6
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• pp.320-328
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• 2003

A specimen of Cu-35%Sn alloy has been subjected to the unidirectional heat treatment in an attempt to examine the evolution of microstructures under varying thermal conditions. The specimen was cast in the form of a cylinder 10 mm in diameter and 200 mm in length, which was then installed in the temperature gradient field established inside a vertical tube furnace. The furnace temperature was adjusted to make the upper part at $750^{\circ}C$ and bottom end part at $300^{\circ}C$ of the specimen. The experiment was terminated by dropping it into water after the 30 minutes holding at given temperature. By the rapid cooling, the high temperature phases, ${\gamma}$ and ${\zeta}$, were retained at ambient temperature with some of ${\gamma}$ phase transformed to ${\varepsilon}$ phase, especially at the grain boundaries of ${\gamma}$ phase. The presence of ${\varepsilon}$ phase was found to determine the nature of phase transformations of the ${\zeta}$ phase undergoes upon cooling. In the close area of the ${\varepsilon}$ phase, ${\varepsilon}$ phase grew separately out of ${\zeta}$, and adds to the preexisting ${\varepsilon}$ whereas in areas away from ${\varepsilon}$, both ${\delta}$ and ${\varepsilon}$ grew simultaneously out of ${\zeta}$, and formed a lamella eutectoid structure. The transformation to ${\delta}$ was found to occur only in slow cooling. The hardness on each phase showed that the retained phases, ${\gamma}$ and ${\zeta}$, could be plastically deformed without brittle fracture while the phases, ${\varepsilon}$ and ${\delta}$, were too brittle to be deformed.

• Journal of Astronomy and Space Sciences
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• v.29 no.3
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• pp.321-328
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• 2012

We have designed a 30 cm cryogenic space infrared telescope for astronomical observation. The telescope is designed to observe in the wavelength range of 0.5~2.1 ${\mu}m$, when it is cooled down to 77 K. The result of the preliminary design of the support structure and support method of the mirror of a 30 cm cryogenic space infrared telescope is shown in this paper. As a Cassegrain prescription, the optical system of a 30 cm cryogenic space infrared telescope has a focal ratio of f/3.1 with a 300 mm primary mirror (M-1) and 113 mm secondary mirror (M-2). The material of the whole structure including mirrors is aluminum alloy (Al6061-T6). Flexures that can withstand random vibration were designed, and it was validated through opto-mechanical analysis that both primary and secondary mirrors, which are assembled in the support structure, meet the requirement of root mean square wavefront error < ${\lambda}/8$ for all gravity direction. Additionally, when the M-1 and flexures are assembled by bolts, the effect of thermal stress occurring from a stainless steel bolt when cooled and bolt torque on the M-1 was analyzed.

• Journal of Ceramic Processing Research
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• v.13 no.spc2
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• pp.328-331
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• 2012

With the recent development of super-precision optical instruments, camera modules for devices, such as portable terminals and digital camera lenses, are increasingly being used. Since an optical lens is usually produced by high-temperature compression molding methods using tungsten carbide (WC) alloy molding cores, it is necessary to develop and study technology for super-precision processing of molding cores and coatings for the core surface. In this study, Rhenium-Iridium (Re-Ir) thin films were deposited onto a WC molding core using a sputtering system. The Re-Ir thin films were prepared by a multi-target sputtering technique, using iridium, rhenium, and chromium as the sources. Argon and nitrogen were introduced through an inlet into the chamber to be the plasma and reactive gases. The Re-Ir thin films were prepared with targets having a composition ratio of 30 : 70, and the Re-Ir thin films were formed with a 240 nm thickness. Re-Ir thin films on WC molding core were analyzed by scanning electron microscope (SEM), atomic force microscope (AFM), and Ra (the arithmetical average surface roughness). Also, adhesion strength and coefficient friction of Re-Ir thin films were examined. The Re-Ir coating technique has received intensive attention in the coating processes field because of promising features, such as hardness, high elasticity, abrasion resistance and mechanical stability that result from the process. Re-Ir coating technique has also been applied widely in industrial and biomedical applications. In this study, WC molding core was manufactured, using high-performance precision machining and the effects of the Re-Ir coating on the surface roughness.