• Journal of Korea Foundry Society
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• v.31 no.2
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• pp.79-82
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• 2011

Various grain refining alloying elements such as Sr, TiB, and Ca were added to AZ91D and their effects on the mechanical properties and mold filling ability were investigated. The average grain sizes of those alloys were significantly reduced by the small amounts of the alloying elements. Ca addition was the most remarkably effective in reducing the grain size, however it was found to deteriorate the mold filling ability and tensile properties. TiB addition was observed to be the most efficient for both grain refinement and mold filling.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.97-97
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• 2012

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.694-699
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• 2002

In autobody assembly, thin-wall, tubular connections have been used for the frame structure. Recent interest in light materials, such as aluminum or magnesium alloys, has been rapidly growing for weight reduction and fuel efficiency. Due to higher thermal expansion coefficient, low stiffness/strength, and low softening temperature of aluminum and magnesium alloys, control of welding-induced distortion in these connections becomes a critical issue. In this study, the material sensitivity to welding distortion was investigated using a T-tubular connection of three types materials; low carbon steel (A500 Gr. A), aluminum alloy (5456-H116) and magnesium alloy (AZ91C-T6). An uncoupled thermal and mechanical finite element analysis scheme using the ABAQUS software program was developed to model and simulate the welding process, welding procedure and material behaviors. The predicted angular distortions were correlated to the cumulative plastic strains. A unique relationship between distortion and plastic strains exists for all three materials studied. The amount of distortion is proportional to the magnitude and distribution of the cumulative plastic strains in the weldment. The magnesium alloy has the highest distortion sensitivity, followed by the other two materials with the steel connection having the least distortion. Results from studies of thin-aluminum plates show that welding distortion can be minimized by reducing the cumulative plastic strains by preventing heat diffusion into the base metal using a strong heat sink placed directly beneath the weld. A rapid cooling method is recommended to reduce welding distortion of magnesium tubular connections.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.3
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• pp.29-34
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• 2012

This paper reports some experimental results in high speed rigid tapping of magnesium alloy(AZ91D). M3 spiral tap and high speed spindle tapping center of gantry type were used in experiments and thrust forces were measured. The experimental results indicate that the thrust forces are proportional to the spindle speed and depth of cut. The thrust forces increase as the depth of cut increases. M3 Tapping was achieved at the spindle speed of 10,000rpm, depth of cut of 1.5D and total stroke of 32mm.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.10
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• pp.77-83
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• 2002

Magnesium alloys casting are gaining increased acceptance in the automotive and electronic industeries and die casting is the most efficient method of manufacturing such mass produced parts. This study has been investigated the microstructures and mechanical properties of Mg-9Al-lZn alloy fabricated by die casting process for development of air bag case. The microstructure of die casted specimen were composed of pro-eutectic magnesium solid solution and $\beta$(Mg17Al12) precipitates. The tensile strength of as-fabricated Mg-9Al-lZn alloy revealed 231.4MPa. It was found that Mg-9Al-lZn alloy have good corrosion resistance in electrochemical polarization test.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.123.1-123.1
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• 2016

마그네슘 및 마그네슘 합금은 차세대 경량 구조 재료로서 많은 각광을 받고 있지만, 상대적으로 높은 반응성과 낮은 부식저항성으로 인해 사용에 제한이 있어왔다. 최근 연구결과에 따르면, 상용으로 널리 쓰이는 AZ91 마그네슘합금에 Ca과 Y을 복합 첨가하였을 경우 마그네슘합금의 발화저항성을 크게 향상시키는 것으로 알려져 있어 마그네슘합금의 적용분야를 확대할 수 있을 것으로 많은 기대를 받고 있다. 그러나 이러한 합금이 실제적으로 적용되기 위해서는 반드시 내식성에 대한 평가와 연구가 수반되어야 하며, 이를 통해 부식거동에 대한 메커니즘을 규명함으로써 고내식 합금 개발을 위한 연구로 이어질 수 있도록 해야 한다. 따라서 본 연구에서는 기존의 AZ91D 합금과 Ca, Y이 복합 첨가된 modified AZ91D 합금 다이캐스트 주조재에 대하여 내식성을 평가 및 비교하고 부식 메커니즘을 규명하기 위한 미세조직 분석 및 부식거동 평가를 실시하였다. 본 연구결과에 따르면, AZ91D 합금 주조재에 Ca과 Y을 복합첨가한 합금은 발화저항성 뿐만 아니라 내식성도 크게 향상되는 것으로 나타났다. 이러한 내식성의 향상은 Ca과 Y의 첨가에 따른 Fe와 같은 불순물의 영향 감소 및 Ca과 Y이 포함된 이차상의 형성으로 인한 상과 기지간의 부식 전위의 차이 감소로 인한 미세 갈바닉 부식 발생의 감소 효과에 기인한 것으로 판단된다.

• Composites Research
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• v.33 no.5
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• pp.247-250
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• 2020

In this study, the possibility of manufacturing a magnesium (Mg) composites reinforced with continuous silicon carbide (SiC) fibers was examined using a liquid pressing process. We fabricated uniformly dispersed SiC fiberAZ91 composites using a liquid phase pressing process. Furthermore, the precipitates were controlled through heat treatment. As a continuous Mg₂Si phase was formed at the interface between the SiC fiber and the AZ91 matrix alloy, the interfacial bonding strength was improved. The tensile strength at room temperature of the prepared composite was 479 MPa, showing excellent mechanical properties.

• Composites Research
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• v.25 no.4
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• pp.93-97
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• 2012

Carbon nano fibers (CNFs) reinforced magnesium alloy (AZ91) matrix composites have been fabricated by liquid pressing process. In order to improve the dispersibility of CNFs and the wettability with magnesium alloy melt, CNFs were mixed with submicron sized SiC particles ($SiC_p$). Also, the mixture of CNFs and $SiC_p$ were coated with Ni by electroless plating. In liquid pressing process, AZ91 melts have been pressed hydrostatically and infiltrated into three reinforcement preforms of only CNFs, the mixture of CNFs and $SiC_p$ (CNF+$SiC_p$), and Ni coated CNFs and $SiC_p$ ((CNF+$SiC_p$)/Ni). Some CNFs agglomerates were observed in only CNFs reinforced composite. In cases of the composites reinforce with CNF+$SiC_p$ and (CNF+$SiC_p$)/Ni, CNFs were dispersed homogeneously in the matrix, which resulted in the improvement of mechanical properties. The compressive strengths of CNF+$SiC_p$ and (CNF+$SiC_p$)/Ni reinforced composites were 38% and 28% higher than that of only CNFs composite.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.429-432
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• 2009

The influence of the subsequent-annealing (SA) treatment on plasma electrolytic oxidation (PEO)-treated Mg-based alloy was investigated and the dependence of the dehydration reaction on the SA temperature was also studied. For this purpose, a series of the SA treatments were carried out on the coated samples at two different temperatures, i.e. 423 and 523 K for 10 h. In contrast to the sample without SA treatment, the sample annealed at 523 K exhibited a significant difference in term of surface morphology since the MgO content in the oxide layer increased with increasing SA temperature. With increasing SA temperature, the dehydration of $Mg(OH)_2$ led to the increase in the relative amount of the MgO, which was a hard phase. From the nano-indentation results, the applied loads of the samples were seen to increase as SA temperature increased. However, the corrosion resistance of the sample annealed at 423 K was higher than that of the samples annealed at 523 K.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.882-885
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• 2002

Magnesium alloys are very attractive materials for appling to the development of autemobile parts or electric goods where light weight and higher stiffness. Due to higher ratio of strength vs. weight and stillness vs. weight, various magnesium alloys are well applied in much weight saving design applications though extrusion or die-casting process. However for the requisites of higher strength and weight savings, some new fabrication processes has been and it can be realized though the aid of injection modeling technology. To obtain the parametric data base for the injection molding process, various experiments were executed for AZ91D magnesium alloy. This paper propose the optimum condition of injection temperature, first and second pressure. the process was lined-up successfully often changing the injection unit. fluid pressure system from the conventional plastic injection molding process.