• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.175-179
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• 2004

Since the formability of AZ31 magnesium alloy is not good in room temperature, it is known that high temperature forming is advantageous. However, many studies are necessary to find the proper forming temperature for Mg alloy. In this study, experimental and FEM analysis are performed to investigate the forming temperature for AZ31 sheet. The deep drawing process of square cup is used in forming experiment and FEA. The investigations are performed in three forming temperature, room temperature, $250^{\circ}C\;and\;400^{\circ}C$. The square cup is well formed in $250^{\circ}C$ forming temperature, on the other hand, the crack and failure is presented in corner section in room and $250^{\circ}C$ forming temperature. The main cause is investigated as the effect of hardening range by the experimental and FEM results.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.59-62
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• 2006

Mg alloys have drawn a huge attention in the field of transportation and consumer electronics industries since it is the lightest alloy which could be industrially applicable. Most Mg alloy components have been fabricated by casting method. However, there have been a lot of research activities on the wrought alloys and their plastic forming process recently. The deformation behavior of an AZ31 Mg alloy at the elevated temperature was examined firstly to find out the optimum plastic forming range in terms of temperature and strain rate. During high temperature deformation, AZ31 alloy is usually undergone the dynamic recrystallization which influence the deformation behavior in turn. In the present study, the effect of deformation on dynamic recrystallization of an AZ31 alloy was investigated to clarify the relation between the deformation and recrystallization. In an AZ31 alloy system, the dynamic recrystallization was found to occur continuously. Recrystallized grain size was dependent on the stress level.

• Transactions of Materials Processing
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• v.30 no.1
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• pp.43-48
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• 2021

The success of warm forming of Mg alloy sheet is greatly influenced by friction at elevated temperature, depending on the surface treatment of the tool. The tool coating affected the frictional characteristics of AZ31B Mg alloy sheet at elevated and room temperatures. The frictional behavior of the Mg alloy sheet at room temperature was not significantly affected by surface treatment conditions of the tool, but was significantly affected at elevated temperature. When the contact pressure is high, a few surface-treated tools exhibit a higher coefficient of friction than those without surface treatment. It is important to select the surface treatment conditions of the tool in order to ensure appropriate friction during warm forming of Mg alloy sheet.

• Transactions of Materials Processing
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• v.24 no.6
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• pp.405-410
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• 2015

Sheet-forming of Mg alloys is conducted at elevated temperatures (250℃) due to the low formability at room temperature. The high-temperature process often gives rise to surface damage on the alloy (i.e. galling.) In the current study, the frictional characteristics of DLC coating slid against an AZ31 Mg alloy at various temperatures were investigated. The coating has been used widely for low-friction processes. Dry-sliding friction and galling characteristics of an AZ31 Mg alloy (disk), which slid against uncoated and a DLC-coated STD-61 steel (pin), were investigated using a reciprocating-sliding tribometer at room temperature and 250℃. To represent the real sliding phenomena during a sheet metal forming process, single-stroke tests were used (10mm stroke length) rather than a reciprocating long sliding-distance test. The DLC coating suppressed adhesion between the alloy and the tool steel at room temperature, and exhibited a low friction coefficient. However, during sliding at 250℃, severe adhesion occurred between the two surfaces, which resulted in a high friction coefficient and galling.

• Carbon letters
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• v.13 no.4
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• pp.254-259
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• 2012

Nanoporous non-woven carbon fibers for a gas sensor were prepared from a pitch/polyacrylonitrile (PAN) mixed solution through an electrospinning process and their gas-sensing properties were investigated. In order to create nanoscale pores, magnesium oxide (MgO) powders were added as a pore-forming agent during the mixing of these carbon precursors. The prepared nanoporous carbon fibers derived from the MgO pore-forming agent were characterized by scanning electron microscopy (SEM), $N_2$-adsorption isotherms, and a gas-sensing analysis. The SEM images showed that the MgO powders affected the viscosity of the pitch/PAN solution, which led to the production of beaded fibers. The specific surface area of carbon fibers increased from 2.0 to $763.2m^2/g$ when using this method. The template method therefore improved the porous structure, which allows for more efficient gas adsorption. The sensing ability and the response time for the NO gas adsorption were improved by the increased surface area and micropore fraction. In conclusion, the carbon fibers with high micropore fractions created through the use of MgO as a pore-forming agent exhibited improved NO gas sensitivity.

• Journal of Ginseng Research
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• v.35 no.3
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• pp.301-307
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• 2011

To evaluate the difference in expressing pharmacological effects of ginseng by intestinal microflora between Koreans, metabolic activities of ginseng, ginsenoside $Rb_1$ and $Rg_1$ by 100 fecal specimens were measured. The ${\beta}$-glucosidase activity for p-nitrophenyl-${\beta}$-D-glucopyranoside was 0 to 0.42 mmol/min/mg and its average activity (mean${\pm}$SD) was $0.10{\pm}0.07$ mmol/min/mg. The metabolic activities of ginsenosides Rb1 and Rg1 were 0.01 to 0.42 and 0.01 to 0.38 pmol/min/mg, respectively. Their average activities were $0.25{\pm}0.08$ and $0.15{\pm}0.09$ pmol/min/mg, respectively. The compound K-forming activities from ginsenoside Rb1 and ginseng extract were 0 to 0.11 and 0 to 0.02 pmol/min/mg, respectively. Their average compound K-forming activities were $0.24{\pm}0.09$ pmol/min/ mg and $2.14{\pm}3.66$ fmol/min/mg, respectively. These activities all were not different between males and females, or between ages. Although compound K-forming activity from the aqueous extract of ginseng was low compared to that from ginenoside $Rb_1$, their profiles were similar to those of isolated compounds. Based on these findings, we believe that the intestinal bacterial metabolic activities of ginseng components are variable in individuals and may be used as selection markers for responders to ginseng.

• Transactions of Materials Processing
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• v.19 no.7
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• pp.429-434
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• 2010

The material used is a commercial magnesium based alloy AZ31(Mg-3Al-1Zn) sheet with a thickness of 0.8 mm. Friction tests at various temperatures(R.T. to $200^{\circ}C$) and at various holding forces in the 4 type molds were carried out to investigate the coefficient of friction. A warm drawing process with a local heating and cooling technique was developed in the Mg alloy sheet forming to improve formability because it is very difficult for Mg alloy to deform at room temperature by the conventional method. So, the coefficient of friction at various mold surface treatment conditions in this study was needed to develop the Mg alloy sheet forming technology.

• YAKHAK HOEJI
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• v.35 no.5
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• pp.401-415
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• 1991

Effects of quercetin on the specific and non-specific immune responses were studied in vivo. Quercetin at a dose of 2.5, 5, 10, 20 and 40 mg/kg were orally administered to ICR male mice once daily for 28 consecutive days. Cyclophosphamide was injected intraperitoneally to ICR mice with a single dose of 5 mg/kg 2 days before secondary immunization. Mice were sensitized and challenged with sheep red blood cells (S-RBC). Immune responses were evaluated by humoral and cellular immune reponses and non-specific immune response. The results of this study were summarized as followings; 1. Quercetin significantly decreased the body weight, and introduced the atrophy of liver, spleen and thymus gland dose-dependently, but increased the numbers of white blood cell. 2. Querectin significantly depressed the hemagglutination titer, Arthus reaction and hemolytic plaque forming cell. 3. Quercetin significantly depressed the delayed type hypersensitivity and rosette forming cell. 4. Quercetin at a dose of 2.5, 5 and 40 mg/kg significantly depressed phagocytic activity. 5. Quercetin at a dose of 10 and 20 mg/kg significantly increased natural killer cell activity.

• 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.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1000-1009
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• 2008

Hydro-mechanical forming process has numerous advantages compared to those of a conventional deep drawing process such as an excellent surface quality and low costs of dies. In fact, Hydro-mechanical forming is a desirable forming process for producing complex parts in automotive body components, and it is an excellent candidate for the forming process of aluminum panels. In this research, Hydro-mechanical forming process with a cross shape punch has been studied for Al-Si-Mg alloy sheets. Finite element analysis by LS-Dyna has predicted the deep drawing depth of the aluminum sheets, and the experiment has confirmed that result. Put Abstract text here.