• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.371-374
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• 2009

Die casting process has been used widely for complex automotive products such as the knuckle, arm and etc. Generally, a part fabricated by casting has limited strength due to manufacturing defects by origin such as the dendrite structure and segregation. As an attempt to offer a solution to these problems, forging has been used as an alternative process. However, the forging process provides limited formability for complex shape products. Rheo-forging of metal offers not only superior mechanical strength but also requires significantly lower machine loads than solid forming processes. This paper presents the results of an A356 aluminum alloy sample, which were obtained by experiment and by simulation using DEFORM 3D. Samples of metal parts were subsequently fabricated by using hydraulic press machinery.

• Journal of Powder Materials
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• v.6 no.3
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• pp.231-237
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• 1999

In this study, the characteristics of gas atomized Mg-3wt%Al-1wt%Zn-1wt%MM alloy powders under vacuum condition were investigated. In spite of the low fluidity and easy oxidation of the molten magnesium, the spherical powders could be successfully produced by using a modified three pieces nozzle attached to the gas atomization unit. It was found that most of the solidified powders less than 50$\mu$m in diameter were single crystal and the solidified structure showed a typical dendritic morphology due to supercooling prior to nucleation. The secondary dendrite arm spacing decreased as the size of powders decreased. The Mg-Al-Ce intermetallic compounds with chemically stable phase were found in the interdendritic regions of $\alpha$-Mg. It is considered that formation of the chemically stable phase may possibly affect to improve the corrosion resistance. Therefore, it is expected that the materials formed of these Mg-Al-Zn-MM alloy powders shows better mechanical properties and corrosion resistance due to the structural refinement.

• Journal of Powder Materials
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• v.18 no.4
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• pp.340-346
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• 2011

In order to improve the weak mechanical properties of cast Mg alloys, Mg-$Zn_1Y_2$ (at%) alloy powders were synthesized using gas atomization, a typical rapid solidification process. The powders consist of fine dendrite structures less than 3 ${\mu}m$ in arm spacing. In order to fabricate a bulk form, the Mg powders were compacted using magnetic pulse compaction (MPC) under various processing parameters of pressure and temperature. The effects of the processing parameters on the microstructure and mechanical properties were systematically investigated.

• Journal of Korea Foundry Society
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• v.21 no.6
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• pp.343-349
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• 2001

The effect of cooling rate on the solidification microstructure and segregation behavior of 7075 and 7050 aluminum alloy was investigated. Samples were solidified with cooling rates from 0.3 to $17^{\circ}K/sec$. Using the cooling curves of each sample, liquidus, eutectic and intermetallic reaction temperatures were estimated. The microstructures were characterized in terms of dendrite arm spacing and eutectic volume fraction. The segregation behavior of each alloying element of these alloys in various cooling rates was discussed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.381-384
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• 2001

The combined stirring method to uniform distribution of particle is consisted of two strring force both electro-magnetic stirring generated from induction heating and mechanical stirring with graphite stirrer. PMMC billets were fabricated with the volume fractions ranged from 0% to 20% and particle sizes ranged from 14$\mu\textrm{m}$ to 25$\mu\textrm{m}$. It is important to control the size of primary ${\alpha}$-AI solid particles because it could become the cause of the particle pushing or capture phenomena from the fact that secondary dendrite arm spacing size depends on the cooling rate during the solidification in hypoeutectic AI-Si alloy.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.6 no.3
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• pp.92-97
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• 2007

The overlay welding the automobile where the durability is demanded, it is used in the vessel engine valve, plant valve and pump parts. Cause of damage public opinion one what is thought is the fatigue load due to the opening and shutting operation right time repetition of the engine valve. The damage cause of the engine valve or explanation of destruction mechanism is very difficult. The research which it sees to make clear a overlay welding of Co-alloy by Plasma Transferred Arc Weld Surfacing Process reconsideration fatigue crack initiation and fatigue crack growth mechanism at high temperature.

• Journal of Korea Foundry Society
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• v.18 no.3
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• pp.254-261
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• 1998

Microstructure and mechanical properties of the low pressure die-cast Al wheels were investigated by microscope, image analyzer, NDT (non-destructive test), and tensile test. The variation of SDAS (secondary dendrite arm spacing), porosity per unit area, quality grade, and tensile properties with the mold temperatures were examined. SDAS was gradually decreased with a decrease in temperature. However, the lowest value of porosity per unit area was observed at the mold temperature of $405^{\circ}C$ and the optimum mold temperature was found to be $405^{\circ}C$. Besides, from the observation of pore morphology, it was also found that the pore formation was mainly caused by shrinkage during solidification. The tensile strength, elongation, and impact toughness were markedly decreased, however the yield strength was nearly constant. The decrease of mechanical properties is attributed to the increase of porosity.

• Journal of Korea Foundry Society
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• v.32 no.5
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• pp.225-230
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• 2012

In this study, a more practical and simulation approach which can predict the mechanical properties of aluminum alloys is proposed. First, cooling rate, micro-structure, and mechanical properties of casting product were measured through casting experiment. The relation between cooling rate and SDAS decrease exponentially and the linearly decreasing relation exist between SDAS and mechanical properties. Then, the cooling rate was calculated by casting process simulation and the mechanical properties were predicted by using the relations that were derived through experiment. Experimentally measured mechanical properties and predicted values by simulation were in the range of relatively small difference. The mechanical properties of various Al alloys are expected to be predicted by the casting process simulation before actual casting.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.10a
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• pp.629-630
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• 2006

• Journal of Korea Foundry Society
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• v.12 no.3
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• pp.203-209
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• 1992

Directional solidification of Al-Ti peritetic alloys was carried out using Upward Continuous Casting Process. The morphology of a solid-liquid interface and solidification microstructures were investigated under various crystal growing conditions. The experimental results were compared with those attained by the Bridgman method. The cell spacing of the Al-Ti peritetic alloys and the primary dendrite arm spacing of the Al-Ti peritetic alloys decreased with an increase in pulling speed. The primary ${\beta}$ phase of the Al-Cr and Al-Ti peritectic alloys did not appear in solidification microstructures because of the depleted solute contents in the melt ahead of the solid-liquid interface.