• Metals and materials international
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• v.24 no.6
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• pp.1262-1274
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• 2018

The inhibition of gravity segregation has been a long-standing challenge in fabrication and applications of homogeneous immiscible alloys. Therefore, the effect of rare-earth La on the gravity segregation of Al-Bi immiscible alloys was investigated to understand the homogenization mechanism. The results showed that the addition of La can completely suppress the gravity segregation. This is attributed to the nucleation of Bi-rich liquid phase on the in-situ produced $LaBi_2$ phase and the change of the shape of $LaBi_2@Bi$ droplets. In addition, a novel strategy is developed to prepare the homogeneous immiscible alloys through the addition of rare-earth elements. This strategy not only is applicable to other immiscible alloys, but also is conducive to finding more elements to suppress the gravity segregation. This study provided a useful reference for the fabrication of the homogeneous immiscible alloys.

• Journal of Korea Foundry Society
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• v.19 no.1
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• pp.47-53
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• 1999

Squeeze casting process has been used in the field of a commercial manufacturing method, in which metal is enforcedly solidified under pressure enough to prevent the cast defects such as either gas porosity or shrinkage defect. In this paper, to clarify the relationship between applied pressures and macro ${\cdot}$ microstructural behaviors in gravity and direct squeeze casts, specimens were cast by various squeezing pressures during solidification of 7000 series Al wrought alloy in the metal die designed specially. The applied pressures used in this study were 0, 25, 50, and 75 MPa. The microstructural morphologies of squeeze cast were more fine and dense with increasing the applied pressures, because of the greater solidification rate of billet resulting from the applied pressure. A normal segregation phenomenon of an increasing in amount of eutectics towards the center of the billet was observed for squeeze casts, whereas gravity cast showed an inverse segregation phenomenon of an increasing in amount of eutectics towards the edge in the billet. This change in segregation pattern which is normal or inverse is due to a higher radial temperature gradient and reduced time in the semi solid state for squeeze casting.

• Journal of Korea Foundry Society
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• v.10 no.4
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• pp.316-323
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• 1990

To improve free-cutting property, fine Pb, Bi particles is necessary to be distributed evenly in Al-Cu alloy. The control of added element size and distribution are very difficult because of the insolubility and gravity segregation of Pb, Bi in the matrix. Therefore, in this study, mechanical stirring of the melt, inert gasbubbling, the addition of degasser are used for the fine distribution of Pb, Bi particles. The best distribution are obtained by stirring with 500 rpm for 10min., Ar gas bubbling with 600cc/min for 5min. and degassing with 0.8wt% degasser. As increasing cooling rate, fine grain size and finely dispersed particles were observed. The optimum pouring temperature was $650^{\circ}C$.

• Journal of Korea Foundry Society
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• v.17 no.2
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• pp.180-187
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• 1997

The influence of solidification condition on the segregation of SiC particles in the $Al-xSi/6wt%SiC_p$(x: 6, 10, 14, 18${\cdot}$wt%) composites was investigated in the study. The results are as follows: 1) During the counter-gravity unidirectional solidification of $Al-Si/SiC_p$ composites melt, most of the SiC particles are pushed to the top of the casting. 2) The SiC particles pushing in the $Al-Si/SiC_p$ composite melts are not observed, when the interface velocity of melts increases more than 1.41 ${\mu}m/sec$. 3) The SiC particles are entrapped in the interdendrite regions, when the sizes of SiC particles in the $Al-Si/SiC_p$ composites are large than ${\varphi}22{\mu}m$.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.902-905
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• 2000

As the manufacturing processes of automotive engine piston, gravity die-casting, squeeze casting, hot forging and powder forging process are generally used for the various specifications. As the semi-solid forming(SSF) is compared with conventional casting such as gravity die-casting and squeeze casting for the characteristics of its process, the product without inner defects such as gas porosity and segregation can be obtained and its microstructure is globular grain. In SSF process, the materials are heated up to the temperature between the solvus and liquidus line at which the materials exists in the form of liquid-solid mixture. In this time, Discussion is given about reheating process of row material and results are presented regarding accurate temperature and process variables controlling for right solid fractions.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.747-750
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• 2004

Lightweight concrete is known for its advantage of reducing the self-weight of the structures, reducing the areas of sectional members as well as making the construction convenient. Thus the construction cost can be saved when applied. to . structures such as long-span bridge and high rise buildings. However, the lightweight concrete requires specific design mix method that is quite different from the typical concrete, since using the typical mix method would give rise the material segregation as well as lower the strength by the reduced weight of the aggregate. In order to avoid such problems, it is recommended to apply the design mix method of high performance self-compacting concrete for the lightweight concrete. Therefore, this study introduces a production of self-compacting concrete, PF-modified and improved version of Nan-Su's design mix method of self-compacting concrete. Through a series of test mixes conducted during the study, the quality of the concrete at its fresh condition has been evaluated per the 2nd class rating standards of self-compacting concrete published by JSCE, especially focused in its fluidity, segregation resistance ability, and filling ability.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.3
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• pp.151-158
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• 2007

The recent government policy for environment is pursuing for a circular waste control system not only to reduce waste as much as possible but also to vigorously use the already produced waste. Copper slag has a higher fineness modulus and a greater specific gravity than natural aggregate. but when the substitutive ratio of fine aggregate is higher than 30%, material segregation occurs by bleeding. Thus, in this study, the strength and the physical properties were tested for the specimens manufactured by varying the types of admixtures, and the substitutive ratio of copper slag to suppress material segregation occurring due to the bleeding of concrete using copper slag as the substitutive material of fine aggregate and to find the adequate substitutive ratio of copper slag.

• Journal of Korea Foundry Society
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• v.12 no.4
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• pp.346-354
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• 1992

In Al-Pb monotectic alloys Pb particles are difficult to uniformly distribute over the Al matrix because of the gravity segregation of pb element. Therefore the effects of centrifugally spray casting process on microstructures and distributions of Pb particle were investigated. As the preform thickened the sine of Pb particle became larger, the amount of porosity became lower and microstructures showed the change from spray-deposition microstructures in the lower part of the preform to spray-casting microstructures in the upper part of it. The size of Pb particles, amount of porosity and splat layer boundaries in hot forged preform showed still less than of as-deposited preform.

• Journal of Korea Foundry Society
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• v.10 no.5
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• pp.392-398
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• 1990

To improve free-cutting property, fine Pb, Bi particles is necessary to be distributed evenly in Al-Cu alloy. The control of added element size and distribution are very difficult because of the physical properties of Pb, Bi. The effect of master alloy compositions on microstructure and particle distribution was investigated. The ribbon shape of Pb-50wt% Bi master alloy showed the best results. And Ti addition improved even distribution of Pb, Bi particles. Particles grown from $L_2$ phase were considered to be the Pb, Bi compound.