• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1346-1348
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• 2001

Generally, Invar alloy shows very low thermal expansion characteristics, lower than $2{\times}10^{-6}$/K approximately. To apply Fe-Ni-Co-C Invar alloy as a core material for large ampacity transmission line we studied the effects of magnetic properties on coefficient of thermal expansion. The coefficient of thermal expansion(CTE) suddenly decreases with addition of a little carbon(0.08%), increases with the increasing carbon and has a constant value at the composition over than 1.0%C. The trend of Curie temperature change with carbon is similar with that of CTE. Therefore, the CTE has a linear relationship with Curie temperature. However, the CTE linearly decreases with the ratio of saturation magnetization and Curie temperature(${\sigma}_s/T_c$).

• Journal of Korea Foundry Society
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• v.21 no.5
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• pp.286-289
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• 2001

The glass formation behavior was investigated in the melt spun Zr-Ti-Cu-Ni-X (X=B, P and Si) ribbons. The magnitude of supercooled liquid region of Zr-Ti-Cu-Ni alloy increased with an addition of alloying element. The glass transition temperature and the crystallization temperature increased and the magnitude of supercooled liquid region decreased with increasing the content of alloying elements. The largest supercooled liquid region was observed in the Si containing alloy. This is believed to be due to the dense atom packing with the optimum atomic size ratio of constituent elements.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.355-356
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• 2009

The change of thermal expansion and mechanical behaviors by cold working has been investigated in Fe-29%Ni-17%Co low thermal expansion Kovar alloy. Fe-29%Ni-17%Co alloy was cold rolled gradually and prepared to plates having reduction ratio of 0%, 20%, 40%, 60%, and 80%. Annealing effect on the properties was also studied. Thermal expansion was measured from $25^{\circ}C$ to $600^{\circ}C$ with a heating rate of $5^{\circ}C$/min by using vacuum differential dilatometer. It was found that thermal expansion coefficient ($\alpha_{30{\sim}400}$) slightly decreased (reduction ration of 20%) and then remarkably increased (above reduction ration of 40%) with increasing reduction ratio of cold rolling. Thermal expansion coefficient ($\alpha_{30{\sim}400}$) was sharply decreased after annealing heat-treatment. Yield and tensile strengths were continuously increased and elongation was decreased by cold roiling. Microstructural observation and X-ray diffraction analysis results showed that the $\alpha$ phase significantly increased as the reduction ratio increased. The slight decrease of thermal expansion coefficient bellow reduction ration of 20% could be explained by the destroying short-range ordering and the decreasing of grain size. The significant increase of thermal expansion coefficient with cold rolling mainly attributed to the appearance of $\alpha$ phase. The correlation between the microstructural cause and invar phenomena for the low thermal expansion behavior was also discussed.

• Journal of the Korean Ceramic Society
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• v.46 no.3
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• pp.295-300
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• 2009

The crystal structure of surface coatings on Al1050 alloy by PEO (Plasma Electrolytic Oxidation), were investigated. The electrolyte for PEO was Na-Si-P system solution. The main crystalline phase were $\gamma$-alumina and $\alpha$-alumina. Crystallinity was increased with applied voltage and applied time. The dominant crystalline phase were affected not only chemical composition of Al alloy substrate and electrolyte, but also the +/- ratio of applied voltage.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.6
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• pp.804-811
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• 2010

The fatigue crack propagation is stochastic in nature, because the variables affecting the fatigue behavior are random and have uncertainty. Therefore, the fatigue life prediction is critical for the design and the maintenance of many structural components. In this study, fatigue experiments are conducted on the specimens of magnesium alloy AZ31 under various conditions such as thickness of specimen, the load ratio and the loading condition. The probability distribution fit to the fatigue failure life are investigated through a probability plot paper by these conditions. The probabilities of failure at various conditions are also estimated. The fatigue design life is predicted by using the Weibull distribution.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.116-119
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• 2007

The application of light weight materials, such as aluminum alloy, has been limited due of their poor formability. Especially, aluminum alloy tube has limited expansion capability at most 15% at room temperature. New manufacturing process, called hot air forming, is introduced to apply aluminum tube to the automotive suspension components which have complex shape and require high expansion ratio about 40%. The process is carried out at the elevated temperature above $500^{\circ}C$, so numerous material properties and process parameters related to the high temperature should be investigated and determined to get a sound product. In this study, the effect of thermal properties and forming parameters such as the temperature of tool, axial feeding and gas pressure are analyzed by using explicit finite element method.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.4
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• pp.570-577
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• 2008

Magnesium alloys are potentially useful as structural materials due to higher strength/weight ratio, heat conductivity and recyclability compared to other alloys. These alloys have attracted the interest of modern manufacturing such as the automobile, computer, communication and consumer electronic appliances industries. Hence welding techniques are required to be developed for these applications. Laser are known to be an excellent tool for them. This paper presents the laser weldability of AZ31 magnesium alloy with CW Nd:YAG laser. The low viscosity and surface tension of the melt pool make magnesium more difficult to weld than steel. As a result of this study, optimal process parameters could be obtained without weld defects. Also it was certain that cutting methods had influence on butt weldability.

• Journal of Korea Foundry Society
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• v.25 no.3
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• pp.128-133
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• 2005

The effects of Mn and Cr on the crystallization behaviors of Fe-bearing intennetallics in A356 alloy were studied. Coarse and acicular ${\beta}-Al_{5}$FeSi phase in A356-0.20wt.%Fe alloy was modified into small ${\alpha}$-Al(Fe,Mn)Si and ${\alpha}$-Al(Fe,Cr)Si phases in response to Mn and Cr addition, respectively. Increasing of Mn addition amount elevates the crystallizing temperature of ${\alpha}$-Al(Fe,Mn)Si and the Mn/Fe ratio in the ${\alpha}$-Al(Fe,Mn)Si. Cr is more effective to modify ${\beta}-Al_{5}$FeSi in comparison with Mn. ${\alpha}$-Al(Fe,Mn)Si phase had BCC/SC dual structure.

• Transactions of Materials Processing
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• v.21 no.4
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• pp.221-227
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• 2012

The automotive and electronic industries have seriously considered the use of magnesium alloys because of their excellent properties such as strength to weight ratio, EMI shielding capability, etc. However, it is difficult to form magnesium alloys at room temperature because of the mechanical deformation related to twinning. Hence, magnesium alloys are normally formed at elevated temperatures. In this study, a temperature dependent constitutive model, the C-H/V model, for the magnesium alloy AZ31B sheet is proposed. A hardening law based on nonlinear kinematic and H/V(Hollomon/Voce) hardening model is used to properly characterize the Bauschinger effect and the stabilization of the flow stress. Material parameters were determined from a series of uni-axial cyclic experiments(C-T-C) with the temperature ranging between 150 and $250^{\circ}C$. The developed models are fit to experimental data and a comparison is made.

• Transactions of Materials Processing
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• v.17 no.7
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• pp.473-480
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• 2008

Sheet metal forming of Mg alloy is usually performed at elevated temperature because of the low formability at room temperature. Therefore, strain rates affected with the forming temperature and speed must be considered as important factor about formability. Effects of process parameters such as various temperatures and forming speeds were investigated in circular cup deep drawing. From the experimental results, it is known that LDR (Limit Drawing Ratio) increase as the strain rate increase. On the contrary, the FLD (Forming Limit Diagram) shows lower value as faster strain rate. Therefore, anisotropy values are investigated according to the temperature and strain rates at each forming temperature. R-values also represent higher value as faster strain rate. It is known that the formability can be different with the deformation mode on warm forming of AZ31 alloy sheet.