• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1999.06a
• /
• pp.15-32
• /
• 1999

A relationship between stress and stain is very important to design a die to avoid defects of products during semi-solid forming process. Since the liquid will be of eutectic composition in alloys liquid segregation will result in significant or undesirable situation. The materials used in this experiment are A 357. A390, Al2024 alloys that is fabricated by the electro-magnetic stirring process from Pechiney in France. The compression test was performed by induction heating equipment and MTS. In order to prevent the liquid segregation these measured temperature would be useful to control of strain rate during compression test. The liquid segregation is controlled as change of the strain rate and solid fraction during the compression process, The characteristics of flow between solid and liquid phase considering liquid segregation is examined through the above experiments. In the case of medium and high volume fractions of solid the distribution of strain rate is calculated by using compression test data of semi-solid materials (SSM). The thixoforming experiments with the designed die are carried out successfully. The die filling patterns of SSM for variation of die temperature and pressing force have been investigated. The hardness of the thixoformed scroll products is evaluated in terms of the microstructure for each position.

• Microbiology and Biotechnology Letters
• /
• v.26 no.4
• /
• pp.369-372
• /
• 1998

Microbial insecticide formulations were prepared by liquid and semi-solid fermentations using Bacillus thuringiensis subsp. kurstaki, HL-106 (BTK-HL106), B. thuringiensis subsp. israelensis HL-63 (BTI-HL63) and B. sphaericus 1593 (BS-1593) strains. The liquid fermentation medium contained molasses 2%, dextrose 1.5%, peptone 2%, D-xylose 0.025%, CaCl$_2$ 0.1%, K$_2$HPO$_4$ 0.1%, KH$_2$PO$_4$ 0.1%, MgSO$_4$$.$7H$_2$O 0.03%, FeSO$_4$$.$7H$_2$O 0.002%, ZnSO$_4$$.$7H$_2$O 0.02%. The composition of the semi-solid fermentation medium was rice bran 45.2%, zeolite 31%, yeast powder 0.02%, corn powder 5%, dextrose 3%, lime 0.3%, NaCl 0.06%, CaCl$_2$ 0.02%, and H$_2$O 15.42%. Insecticide formulations produced in the liquid fermentation named BTK-HL106, BTI-HL63 and BS-1593 pesticides and those in the semi-solid fermentation were designated as BTK-HL106-1, BTI-HL63-1 and BS-1593-1 pesticides, respectively. The number of spore (endotoxin crystals) was 2.65${\times}$10$\^$9/ spores per $m\ell$ in the BTK-HL106 and 3.5${\times}$10$\^$10/ in the BTK-HL106-1 3.8${\times}$10$\^$9/ spores in the BTI-HL63 and 7.0${\times}$10$\^$10/ in the BTI-HL63-1, and 7.5${\times}$10$\^$9/ in the BS-1593 and 1.4${\times}$10$\^$10/ in the BS-1593-1. The spores in the BS-1593 formulation was produced two times more than the other formulations. The spores in the BTI-HL63-1 were contained twice than those in the BTK-HL106-1, and five times than those in the BS-1593-1. The results indicated that spore (endotoxin crystals) productions in the semi-solid fermentation increased about ten times than those in the liquid fermentations. $LC_{50}$s of the BTI-HL63 and BS-1593 were 4.5 $\mu\textrm{g}$, and those of the BTI-HL63-1 and BS-1593-1 were 1.5 $\mu\textrm{g}$. $LC_{50}$ of the BTK-HL106 was 1.5 mg and that of the BTK-HL106-1 was 0.9 mg. The $LC_{50}$s of the formulations in the semi-solid fermentations showed about two to three times higher than those in the liquid fermentations.

• Journal of Korea Foundry Society
• /
• v.32 no.1
• /
• pp.24-31
• /
• 2012

In this study, semi-solid thin plate of A 356 aluminum alloy was fabricated by using slope plate apparatus and vacuum pressurization. Slope plate was used to produce semi-solid material with spheroidal microstructures. After molten metal was poured into the slope plate connected to the pouring hole of die, semi-solid material flowed into the die cavity by vacuum degree. The primary crystals of the cast metal became spheroidal. In order to increase the working pressure, gas pressurization of U shape was designed for fabrication of thin plate. For 3 bar of gas pressure and 60 mmHg of vacuum degree, thin plate was fabricated without defects on surface.

• Journal of Korea Foundry Society
• /
• v.29 no.5
• /
• pp.213-219
• /
• 2009

Optimum conditions for production of semi-solid Al-Zn-Mg alloy billets was carried out by the Taguchi design method. And, Al-Zn-Mg alloy billets contained Sc (free, 0.1 and 0.3 mass %) were fabricated at optimum conditions. Evolution of microstructure in semi-solid state was investigated through various liquid fractions, holding times and holding temperatures. The Al-Zn-Mg alloy billets reheated at $615^{\circ}C$ during 30min are grain growth and it was fractured due to increasing liquid fraction before quenching. And, during reheating up to $600^{\circ}C$, grain growth of Al-Zn-Mg alloy billets contained Sc (0.1 and 0.3 mass %) was not occurred in comparison with those of Al-Zn-Mg alloy without Sc. It was thought that $Al_3Sc$ phases have a pinning effect in grain boundary and Sc content of 0.1 mass% is able to inhibit grain growth effectively through reheating process.

• Journal of Korea Foundry Society
• /
• v.29 no.3
• /
• pp.144-149
• /
• 2009

In this study, we investigated optimum condition of cooling plate method to obtain semi-solid AM100A Mg alloy with fine and globular morphology. AM100A Mg alloy were hot extruded at $380^{\circ}C$ extrusion temperature under extrusion ratio of 25 : 1 and ram speed of 2.4 mm/sec. Vickers hardness test, optical microscopy, scanning electron microscopy, and image analyzer were performed to identify the optimum conditions of cooling plate method. Optimum conditions of cooling plate method to fabricate semi-solid AM100A Mg alloy with fine and globular microstructures were achieved at a pouring temperature of $602^{\circ}C$ and the angle of cooling plate of 60 degree.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2008.10a
• /
• pp.234-237
• /
• 2008

It was reported that the semi-solid forming process has many advantages over the conventional forming process, such as a long die life, good mechanical properties and energy savings. It is very important, however, to control liquid segregation to gain mechanical property improvement of materials. During forming process, Rheology material has complex characteristics, thixotropic behavior. Also, difference of velocity between solid and liquid in the semi-solid state material makes a liquid segregation and specific stress variation. Therefore, it is difficult for a numerical simulation of the rheology Process to be Performed. General Plastic or fluid dynamic analysis is not suitable for the behavior of rheology material. The behavior and stress of solid particle in the rheology material during forging process is affected by viscosity, temperature and solid fraction. In this study, compression experiments of aluminum alloy were performed under each other tool shape. In addition, the dynamics behavior compare with Okano equation to Power law model which is viscosity equation.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.10a
• /
• pp.667-670
• /
• 2002

Uniform metal-droplet deposition using laser is analyzed. Using the variation principle and modeling the semi-solid phase as a non-Netwonian slurry, this model can greatly save the computational expenses that conventional numerical procedures have suffered from. The simulation results revealed that the developed model could reasonably describe the collision behavior of molten metal with solid surface. Simulations were made with variation of the falling distance and time.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.10a
• /
• pp.199-203
• /
• 1995

The technology of Semi-Solid Forging (SSF) has been actively developed to fabricate near-net- shape products using light and hardly formable materials, the SSF process is composed of slug heating, forming, compression holding and ejecting step. After forming step in SSF, the slug is compressed during a certain holding time in order to be completely filled in the die cavity and be accelerated in solidification rate. The compression holding time that can affect mechanical properties and shape of products is important to make decision, where it is necessary to find overall hert transfer coefficeient properly which has large effect on heat transfer between slug and die. This paper presents the procedure to predict compression holding time of octaining the final shaped part with information of temperature and solid fraction for a cylindrical slug at compression hoiding step in closed-die compression process using heat transfer analysis considering latent heat by means of finite element method. The influence of the predicted compression hoiding time on mechanical properties of products is finally investigated by experiment.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1997.06a
• /
• pp.174-182
• /
• 1997

The technology of Semi-Solid Forging (SSF) has been actively developed to fabricate near-net-shape products using light and hardly formable materials. Generally, the SSF process is composed of slug heating, forming, compression -holding and ejecting step. After forming step in SSF, the slug is compressed during a certain holding time in order to be completely filled in the die cavity and be accelerated in solidification rate. The compression holding time that can affect microstructural characteristics and shape of products is important to make decision, where it is necessary to find overall heat transfer coefficient properly which has large effect on heat transfer between slug and die. This paper presents the procedure to predict compression holding time of obtaining the final shaped part with information of temperature and solid fraction for a cylindrical slug at compression holding step in closed-die compression process using heat transfer analysis considering latent heat by means of finite element method. The influence of the predicted compression holding time on microstructural characteristics of products is finally investigated by experiment.

• Journal of Korea Foundry Society
• /
• v.16 no.6
• /
• pp.556-564
• /
• 1996

Variation of shape and size of solid particles and solute redistribution in Mg-9wt.%Al, AI-4.5wt.% Cu, and AI-7wt.%Si alloys were investigated when they were heated to semi-solid temperatures and held without stirring. In the case of Mg-9wt.% Al and Al-4.5wt.%Cu alloys, the polygonal shaped solid particles were agglomerated with non-uniform distribution, and there were no disappearance of the solid/solid boundary until the end of melting. But in the case of an Al-7wt.%Si alloys, two or three spherical shaped particles were coalesced or separated individually, and the coalesced particles had no solid/solid interface on the contrary to the prevous case. The maximum size of solid particles during isothermal heating at high temperature was smaller than that at lower temperature, but the time required to reach the maximum size at high temperature was shorter than that at lower temperature. The concentrations of main solute atom whose distribution coefficient is lower than 1, decreased in the primary solid particles as the liquid fraction increased, and the gradient of solute concentration was steeper in Mg-9wt.%Al alloy and Al-4.5wt.%Cu alloy than that of Al-7wt.%Si alloy.