• Journal of Welding and Joining
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• v.31 no.3
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• pp.49-53
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• 2013

Recently, studies about application of magnesium alloy sheet to automotive bodies are on the increase. For application to automotive bodies, researches about characteristics of resistance spot welding of magnesium alloy sheet are essential. Electrode life of resistance spot welding of magnesium alloy is very short due to sticking of magnesium alloy to copper alloy electrode. To increase electrode life, most effective method is inserting cover plate between electrode and magnesium sheet. But application of cover plate to actual process is difficult and decreases welding productivity. Process tape supplied automatically as cover plate can minimize lose of productivity and increase welding quality. In this study, resistance spot welding of magnesium alloy is carried out with applying process tape. Acceptable welding current region according to electrode force and welding time is determined.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.4
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• pp.190-195
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• 2012

This study aims to investigate and compare the microstructures and room temperature tensile properties for AZ91 and ECO-AZ91 (AZ91+0.3%CaO) alloys in as-cast, T4 and T6 states, respectively. In as-cast state, the ECO-AZ91 alloy has finer microstructure than the AZ91 alloy. The AZ91 alloy exhibits greater ductility, while YS and UTS are inferior to those of the ECO-AZ91 alloy. After T4 treatment, most of ${\beta}$ compounds disappear in the AZ91 alloy, whereas ${\beta}$ phase is still observed in the ECO-AZ91 alloy due to its enhanced thermal stability, resulting in lower values of ductility and UTS. In T6 state, YS and UTS are better in the ECO-AZ91 alloy.

• Journal of the Korean institute of surface engineering
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• v.44 no.1
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• pp.1-6
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• 2011

A NiW functional alloy plating was investigated as variables of metal ion concentration, complexing agent, temperature, pH and applied current density. Even if numerous studies on reaction mechanism of NiW induced codeposition were carried out during couples of decade, it has not been acceptable reaction mechanism. This study was focused on the effect of the plating variables on the alloy composition in the NiW alloy plating. Applied current density could control mainly the alloy composition rather than other plating variables. It has also been confirmed that the functional alloy plating such as layered or gradient plating was possible by controlling applied current density.

• Journal of the Korean institute of surface engineering
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• v.32 no.4
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• pp.521-530
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• 1999

The corrosion resistance and the hardness of the tin-nickel alloy deposits electroplated in pyrophosphate bath were invesitigated according to electrolysis conditions and microstructure of the alloy. The weight loss of alloy deposits increased with the Sn content of single phase (Ni-Sn) alloy showing the lowest weight loss in the alloy with 54∼57wt% Sn. On the other hand, the multiphase alloy with 35∼42wt% Sn showed the highest one. The CASS test result was consistent with that of immersion test, and was good agreement with the corrosion data of polarization measurements. The hardness of alloy deposits decreased with the increase of Sn ratio in bath due to the grain size increase of the alloy. However, it increased noticeably with decreasing current density in the bath condition of low Sn ratio (0.1)

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.42-45
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• 2007

Recrystallization behavior during ingot-breakdown process of Alloy 718 was investigated with finite element analysis and experimental approaches. In order to analyze microstructural changes during the cogging process of an Alloy 718 ingot, the side-pressing and heat treatment tests were performed at different temperatures and ram speed. From the side-pressing and heat treatment test results, it was found that microstructural changes during hot forging of Alloy 718 ingot greatly influenced on a close interaction between dynamic and static-recrystallization behaviors. A recrystallization model of Alloy 718 was used to predict the complex microstructural variation during continuous heating and forging processes of the cogging, and the predicted grain size and its distribution were compared with the actual cogged Alloy 718 billet.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.846-847
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• 2006

The composite used in this paper was prepared by hot-pressing ball-milled Mg alloy powders, in which NiTi shape memory alloy fibers in a row were sandwiched. The microstructure and property were examined. It is shown that the composite consisted of a homogenous matrix with uniformly distributed NiTi shape memory alloy fibers, recrystallization took place in the Mg alloy matrix which was subjected to plastic deformation an adequate bonding formed between the matrix and fibers; the density and tensile strength of the composite increased after the hot-forging; the hot-forging process is capable of improving properties of the composite.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.720-721
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• 2006

The new alloy$^{1)}$ is made from rapidly solidified Al-Ni-Zr-Ce aluminum alloy powder, and has the following unique mechanical characteristics:(1) The stress-strain curve shows a yield point; (2) The alloy shows high heat resistance; (3) Although the alloy is submicron particle diameter, it shows excellent creep resistance. We observed the micro structures of this new alloy, and it is thought that is based on the following reasons:(1) The dislocation strongly adheres to the alloy's many crystal boundaries;(2) The added alloying elements have a small diffusion coefficient in aluminum;(3) The tiny intermetallic compound particles crystallizing at the grain boundary.

• Journal of Powder Materials
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• v.11 no.5
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• pp.369-375
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• 2004

A new concept of tungsten heavy alloy composite was suggested and manufactured in this study for the kinetic energy penetrator. The composite heavy alloy was composed of two parts, the center was molybdenum added heavy alloy compositions which were designed to promote the self-sharpening effect and outside was conventional heavy alloy in order to sustain the severe stress condition in the muzzle during the firing. The center part showed an intergranular and brittle mode at tungsten/tungsten interfaces by which self-sharpening effect could be activated. On the other hand, that of outside showed conventional ductile fracture mode under high strain rate condition. From the sub-scale penetration test, the depth of penetration in heavy alloy composites showed greater values than those of conventional tungsten heavy alloys. It is suggested that the heavy alloy composite could be considered as one of the future penetrator materials.

• Journal of Powder Materials
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• v.13 no.1 s.54
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• pp.25-32
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• 2006

The alumina dispersion-strengthened (DS) C15715 Cu alloy fabricated by a powder metallurgy route was annealed at temperatures ranging from $800^{\circ}C\;to\;1000^{\circ}C$ in the air and in vacuum. The effect of the annealing on microstructural stability and room-temperature mechanical properties of the alloy was investigated. The microstructure of the cold rolled OS alloy remained stable until the annealing at $900^{\circ}C$ in the air and in vacuum. No recrystallization of original grains occurred, but the dislocation density decreased and newly formed subgrains were observed. The alloy annealed at $1000^{\circ}C$ in the air experienced recrystallization and grain growth took place, however annealing in vacuum at $1000^{\circ}C$ did not cause the microstructural change. The mechanical property of the alloy was changed slightly with the annealing if the microstructure remained stable. However, the strength of the specimen that was recrystallized decreased drastically.

• 한국전기화학회:학술대회논문집
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• 2003.07a
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• pp.83-88
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• 2003

PtRu alloy and $PtRu-WO_3$ nanocomposite thin-film electrodes for methanol electrooxidation were fabricated by means of a sputtering method. The structural and electrochemical properties of well-defined PtRu alloy thin-film electrodes were characterized using X-ray diffraction, Rutherford backscattering spectroscopy. X-ray photoelectron spectroscopy, and electrochemical measurements. The alloy thin-film electrodes were classified as follows: Pt-based and Ru-based alloy structure. Based on structural and electrochemical understanding of the PtRu alloy thin-film electrodes, the well-controlled physical and (electro)chemical properties of $PtRu-WO_3$, showed superior specific current to that of a nanosized PtRu alloy catalyst, The homogeneous dispersion of alloy catalyst and well-formed nanophase structure would lead to an excellent catalytic electrode reaction for high-performance fuel cells. In addition, the enhanced catalytic activity in nanocomposite electrode was found to be closely related to proton transfer in tungsten oxide using in-situ electrochemical transmittance measurement.