• Korean Journal of Metals and Materials
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• v.48 no.5
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• pp.436-444
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• 2010

The hot tear susceptibility of Al alloys was investigated by using a constrained-rod mold designed to quantify 8 types of tear tendency. The severity of the crack was scored by 5 grades on a scale of 0 to 4, with 0 being "no crack formed" and 4 being "complete separation by crack". The Hot Tear Susceptibility index (HTS) which consists of crack type scores and position scores, was proposed to compare the hot tear tendency of Al alloys. A356.0 cast alloy and AA6061 wrought Al alloy showed an HTS value of 27.5 and 53 respectively. The effects of Si, Cu, and Mg content on hot tear tendency were also investigated with a constrained-rod mold. The variation of HTS values with alloying elements represents similar behavior in the variation of the solidification range in a pseudo binary phase diagram.

• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.1
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• pp.47-58
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• 2004

Loss factors of A356, Mn-Cu alloy and aluminum matrix composites reinforced with $SiC_p$ and Ni-coated graphite particles at various contents have been investigated using clamped-free cantilever beam method. The loss factors of half-power bandwidth of the specimens were measured over a wide range of frequencies from 50 to 3300Hz. Among the specimens, Al-10%$SiC_p$-10%$C_p$ showed the highest loss factor at the mode I, while Mn-Cu alloy showed the highest loss factors at the modes II and III. Consequently, at the mode I the Al-10%$SiC_p$--10%$C_p$ showed the loss factor of 0.00093, which is 2.64 and 1.58 times higher than those of A356 and Mn-Cu alloy, respectively.

• Journal of Korea Foundry Society
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• v.17 no.1
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• pp.28-35
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• 1997

SiC whisker and $Al_2O_3-SiO_2$ short fiber reinforced AC8A, AC8B and AC8B(J) marix composites were fabricated by squeeze casting method. Preform deformation, change of reinforcement volumefraction and formation of macro-segregation in two composites were investigated by using micro Vickers hardness test, analysis of macro and micro structures with OM, SEM and EDAX. $Al_2O_3-SiO_2$ short fiber preform manufactured with 5% $SiO_2$ binder in this study was considerably deformed and cracked, nevertheless, the short fibers were distributed homogeneously in the composites. In SiC whisker reinforced composites, on the other hand, preform deforming and cracking were not occurred, however, macro segregation zone formed along the infiltration routes by interface reaction during infiltration of molten metal into the preform was observed at center-low area in the composites. The decrease of hardness in the macro segregation zone resulted from the depletion of Si and Mg atoms.

• Journal of Korea Foundry Society
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• v.14 no.6
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• pp.530-540
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• 1994

Aluminium-silicon alloy(JIS AC8A) matrix composites reinforced with SiC particles were fabricated by spray-cast forming process, and the microstructure of powders and preforms produced were studied by using an optical and scanning electron microscopy. SiC particles were co-sprayed by mixed phase injection method during the spray casting process. Most of the composite powders formed by this mixed phase injection method exhibit morphology of particle-embedded type, and some exhibits the morphology of particle attached type due to additional attachment of the SiC particles on the surface of the powders in flight. The preforms deposited were resulted in dispersed type microstructure. The pre-solidified droplets and the deposited preform of SiC-reinforced aluminium alloy exhibit finer equiaxed grain size than that of unreinforced aluminium alloy. Eutectic silicons of granular type are crystallized at the corner of the aluminum grains in the preforms deposited, and some SiC particles seem to act as nucleation sites for primary/eutectic silicon during solidification. Such primary/eutectic silicons seem to retard grain growth during the continued spray casting process. It is envisaged from the microstructural observations for the deposited preform that the resultant distribution of SiC injected particles in the Al-Si microsturcture is affected by the amount of liquid phase in the top part of the preform and by the solidification rate of the preform deposited.

• The Journal of the Korean dental association
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• v.22 no.9 s.184
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• pp.781-792
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• 1984

The purpose of this experiment was to study the effects of laser on a base metal alloy for dental casting. In this study, microhardness, corrosion resistance, wear resistance, interaction behavior of metal-ceramic interface, and bond strength were tested before and after the laser treatment for metal-ceramic alloy. The conclusion arised from this study are as follows: 1. The hardness of lased area was higher than that of unlased area. 2. The corrosion resistance was higher in lased specimen than in unlased specimen. 3. the wear resistance was higher in Iased specimen than in unlased specimen. 4. The EDAX showed that Mo, Si and Al were increased in lased surface but Ni and Cr not increased. 5. The SEM of lased area revealed a typical microstructure. 6. The bond strength of lased specimen was increased in 11.2% than of unlased specimen.

• Journal of Korea Foundry Society
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• v.15 no.6
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• pp.566-573
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• 1995

In this study, the microstructural characteristics such as primary silicon, eutectic silicon, $SiC_p$ dispersion behavior, compound amount and Si solubility in $Al/SiC_p$ composite fabricated by the squeeze casting under various conditions were investigated systematically. As applied pressure(MPa) increases, cooling rate and compound amount are increased. In gravity casting, the cooling rate of hypereutectic composite is slower than of hypoeutectic composite by exothermic reaction of primary Si crystallization. But the cooling rate of hypereutectic composite is faster than that of hypoeutectic composite fabricated by same applied pressure, because amount of primary Si crystallization in hypereutectic composite was decreased, on the contrary, primary ${\alpha}-Al$ in hypoeutetic composite was increased due to increase of Si solubility in matrix by applied pressure. The crystalized primary silicon in hypereutectic composite fabricated by squeeze casting become more fine than that in non-pressure casting This is because mush zone became narrow due to increase of Si content of eutectic composition by pressure and time for growth of primary silicon got shorter according to applied pressure. It is turned out that eutectic temperature and liquidus are decreased by the increasing of squeeze pressure in all the composite due to thermal unstability of matrix owing to increasing of Si solubility in matrix by the increasing of applied pressure, as indicated in thermal anaiysis(DSC) results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.10
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• pp.2034-2043
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• 2002

The process design to produce a near net shape home-appliance compressor component using semi-solid die casting process is performed. In order to obtain a good component without defects such as liquid segregation and porosity, the relationship between pressure and time, and plunger tip displacement and injection velocity are proposed with repeated trial and error. The effect of the velocity variation in the process parameters on liquid segregation and extraction is investigated to produce the aluminum frame part(a kind of compressor part) with good mechanical properties. The mechanical characteristic of semi-solid die casting formed parts for AlSi7Mg0.65r(A357) and AlSi17Cu4Mg(A390) are investigated with a view to minimizing the occurrence of defects. To investigate of application possibility at industry field, A380 aluminum alloy with 8∼9% silicon contents used for the squeeze casting process. The obtained mechanical properties is compared with semi-solid die casting.

• Journal of Korea Foundry Society
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• v.22 no.4
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• pp.167-173
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• 2002

The hydrogen gas pick-up problem that can occur during Lost Foam Casting was investigated by reduced pressure test and practical Lost Foam Casting. The proper test pressure of reduced pressure test was determined by experiments not to use polystyrene and gas contents of the melt were calculated from density measurement results. The results showed that the hydrogen pick-up increased with the increased amount of polystyrene that was replaced by melt. The hydrogen pick-up was larger in the case of no degassed melt than that of degassed melt. So the hydrogen pick-up depended on the initial hydrogen content of the melt and the contact time of the melt with the decomposed gas phase. The mold evacuation decreased the hydrogen pick-up and increased the flow length of melt during Lost Foam Casting. And the error of calculated hydrogen pick-up was calculated by numerical method.

• Journal of Korea Foundry Society
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• v.32 no.2
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• pp.65-74
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• 2012

In this paper, we present the results of our studies on optimal die design towards development of a vacuum die casting process to fabricate fuel cell bipolar plate with micro-channel array. Cavity and overflow shape is designed by computational filling analysis of MAGMA soft. Optimal die design consists of seven overflows at the end of cavity and three overflows at each side wall of cavity. The molten metal that passed the gate and reached the side wall flowed into the side overflow, no turbulent flow occurred, and the filling behavior and velocity distribution were uniform. In addition, partially solidified molten metal passing through the channel was perfectly eliminated by overflow without back-flow. When vacuum pressure, injection speed of low and high region was 300 mbar, 0.3 m/s and 2.5 m/s respectively with Silafont 36 die casting alloy, sound sample without casting defects was obtained. The experimental results are nearly consistent with simulation results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.193-197
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• 2002

In this study, the casting/forging process was applied to the Shift-Fork, a manual transmission part of automobiles. In the casting experiments, the effects of additives, Sr, Ti＋B and Mg, on the mechanical properties and the microstructure of a cast preform were investigated. When 0.03% Sr were added into the molten aluminum alloy, the finest silicon-structure was observed in the cast preform and the highest tensile strength and elongation accomplished. And when 0.2% Ti＋B were added into the molten Al-Si alloy, the highest values of tensile strength were obtained. The maximum hardness was in case of 0.2% Mg. In the forging experiment, it was confirmed that the optimal configuration of the cast preform could be predicted by FE analysis. To minimize the cost as the press size, the compact shape of preform was proposed to reduce the volume of flash. The modification of shape in designing preform was performed to attain a satisfactory performance in the areas where the mechanical strength were more required. By using FVM(Finite Volume Method) software, it was verified that a proposed casting design was available. To identify the relationship between effective strain and mechanical properties of the final forged product, the compression test was performed. As the result, the tensile strength and elongation of a cast preform were much higher than before forging. The minimum forging temperature was found 40$0^{\circ}C$ to save heating time.