• Transactions of Materials Processing
• /
• v.14 no.4 s.76
• /
• pp.338-350
• /
• 2005

Recently, in the field of automobile industry, to solve the problem of reducing the weight of automobile for the improvement of fuel efficiency and the protection of environment, the aluminum alloy parts have been substituted for the steel parts. However, the aluminum alloy does not have as good mechanical property as the steel part. To improve the mechanical property, the semi-solid die casting process is performed to make automobile parts. In the fabrication of semisolid material the control of the liquid segregation is very important to improve the material properties of aluminum alloy. In the present paper we examine the influence of the liquid segregation by the injection conditions in the semi-solid die casting has been investigated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.10a
• /
• pp.60-63
• /
• 2003

Semi-solid forming is the process of stirring alloy during solidification, making the mixture of liquid and solid, solidifying it, reheating it to the solid-liquid coexistent temperature, and then injecting this semi solid slurry into dies. In the semi-solid die casting process, it is very important to find out the correlation of injection condition, microstructure and mechanical properties. Especially, an improper injection condition is the main cause of liquid segregation and non-homogeneous mechanical properties due to the difference of solid fraction according to the position of the products. To ensure the database requisite to the semi-solid die casting product, it is essential to acquire the mechanical properties considering liquid segregation to the injection condition. In this study, the effect of injection condition on liquid segregation, formability, microstructure and mechanical properties in a thin product was investigated.

• Transactions of Materials Processing
• /
• v.16 no.3 s.93
• /
• pp.178-186
• /
• 2007

Rheo-forging process of aluminum alloy is suitable for large parts of net shape without defects and excellent mechanical properties in comparison with conventional die casting and forging process. To control the microstructure of the product with high mechanical properties in rheo-forming, solid fraction is required to prevent porosity and liquid segregation. Therefore, in rheo-forging process, die shape, pressure type and solid fraction are very important parameters. The defects such as porosity, liquid segregation and unfitting phenomena occur during rheo-forging process. To prevent these defects, mechanical properties and microstructure analysis of samples versus the change of pressure are carried out and the problem and its solutions are proposed. Also, the mechanical properties versus various pressures were compared with and without heat treatment. The alloys used for rheo-forming are A356 and 2024 aluminum alloy. The rheology material is fabricated by electromagnetic process with controlling current and stirring time.

• Journal of Ocean Engineering and Technology
• /
• v.16 no.2
• /
• pp.72-79
• /
• 2002

In this study, time-dependent distributions of temperature and stresses, in the box-column welded from ultra thick plates with center segregation, has been analyzed by the commercial finite element package SYSWELD+, for several types and angles of groove. The major points of investigation are the optimum type and angle of groove that minimize weld stress specially at the center segregation, as well as temperature distribution, residual stresses and changes in the mechanical properties. The results can be summarized as follows; 1) Generally the thermal cycle at the root of groove exhibits relatively rapid cooling pattern, however, most of the other part weldment have a slow cooling pattern in all groove types. 2) Most of the micro-structures of weldment are composed of ferrite and pearlite, meanwhile we could find martensite and bainite locally a the root of the groove. 3) Optimum groove type for high heat input welding of box-column corner is a double groove type, and the optimum angle for the groove is 30~$45^{\circ}$ that minimize deformation and weld stress at the center segregation.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2015.08a
• /
• pp.60-60
• /
• 2015

Nanosheets of graphene and related 2D materials have attracted much attention due to excellent physical, chemical and mechanical properties. Single-layer graphene (SLG) was first synthesized by Blakely et al in 1974 [1]. Following his achievements, we initiated the growth and characterization of graphene and h-BN on metal substrates using surface segregation and precipitation in 1980s [2,3]. There are three important steps for nanosheet growth; surface segregation of dopants, surface reaction for monolayer phase, and subsequent 3-D growth (surface precipitation). Surface phase transition was clearly demonstrated on C-doped Ni(111) by in situ XPS at elevated temperatures [4]. The growth mode was clarified by inelastic background analysis [5]. The surface segregation approach has been applied to C-doped Pt(111) and Pd(111), and controllable growth of SLG has been demonstrated successfully [6]. Recently we proposed a promising method for producing SLG fully covering an entire substrate using Ni films deposited on graphite substrates [7]. A universal method for layer counting has been proposed [8]. In this paper, we will focus on the effect of competitive surface-site occupation between carbon and other surface-active impurities on the graphene growth. It is known that S is a typical impurity of metals and the most surface-active element. The surface sites shall be occupied by S through surface segregation. In the case of Ni(110), it is confirmed by AES and STM that the available surface sites is nearly occupied by S with a centered $2{\times}2$ arrangement. When Ni(110) is doped with C, surface segregation of C may be interfered by surface active elements like S. In this case, nanoscopic characterization has discovered a preferred directional growth of SLG, exhibiting a square-like shape (Fig. 1). Also the detailed characterization methodologies for graphene and h-BN nanosheets, including AFM, STM, KPFM, AES, HIM and XPS shall be discussed.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.923-926
• /
• 2008

Currently more high flow and high performance concrete is used for construction of buildings in the world. However, when high flow and high performance concrete put high performance water reducing agent in quantity to improve flow, it has a negative effect on concrete structures since segregation arises from it though flow will be improved. There are naked-eye observation, coarse aggregate washing test, L Flow test for permeation among reinforcing rods and measurement of viscosity to judge concrete segregation resistance. However, it is difficult to apply them to practical affairs since they are very complicated and troublesome. Therefore, the study analyzed EIS dividing slump flow value into slump value, how to valuate concrete segregation resistance more easily, on the basis of the existing reference materials to propose EIS. As the results, in the event of high flow concrete, it is desirable that EIS value is prescribed to be less than 2.5 at the time of managing segregation. Also, at the time of prescribing EIS with performance, it is judged that it is desirable to manage segregation as less than 2.2 (Grade 1), 2.2$\sim$2.4 (Grade 2) and more than 2.6 (Grade 3).

• Journal of Preventive Medicine and Public Health
• /
• v.22 no.4 s.28
• /
• pp.474-479
• /
• 1989

This research was conducted to evaluate the effect of improvement in work environment and of segregation in a fluorescent lamp manufacturing factory. Among the total of 80 workers, 8 workers whose mercury concentration in urine reached a hazardous level ($200-299{\mu}g/l$) were moved to mercury free workplace. The follow-up examination for their mercury concentration in urine was done three times ; on May 3, 1988, September 1, 1988 and April 3, 1989. The results were as follows : 1. Mercury concentration in the air was reduced from 0.140 to 0.107 $mg/m^3$ in 4 months, and to $0.087mg/m^3$ in one year after environmental improvement in workplace. However the level still exceeded the Threshold Limit Value. 2. The geometric mean of urinary mercury concentration among 80 workers was $173.0{\mu}g/l\;(5.1{\sim}458.6{\mu}g/l$). The distribution of workers according to urinary mercury concentration showed that 9 workers (11.2%) were above the mercury poisoning level ($300{\mu}g/l$), 24 workers (30.0%) were $200-299{\mu}g/l$, 35 workers (43.8%) were $50-199{\mu}g/l$, and 12 workers (15.0%) were below 50 ${\mu}g/l$. 3. Among the 24 workers whose urinary mercury concentration was 200-299 $50-199{\mu}g/l$, 8 were able to be followed up. Their mean urinary mercury concentration before segregation was $244.9{\mu}g/l$, but decreased to $151.4{\mu}g/l$ in four months, $128.8{\mu}g/l$ in six months, and $46.8{\mu}g/l$ in one year after segregation.

• Journal of Magnetics
• /
• v.4 no.1
• /
• pp.5-9
• /
• 1999

Effect of sulfur segregation on tertiary recrystallization and magnetic induction during final annealing was investigated in a 3% Si-Fe electrical strip containing 6 ppm(LS) and 15 ppm(HS) sulfur. During final annealing, Auger peak height of segregated sulfur on the surface of the strips reached a maximum, and then decreased to low level with increasing annealing time, which is attributed to sulfur segregation and evaporation. The magnetic induction of the thin-gauged 3% Si strip was inversely proportional to the Auger peak height of segregated sulfur on the surface. The overall profile for surface segregation of sulfur and B10 was observed, irrespective of sulfur content in Si-Fe strips, but the peaks of LS strips appeared earlier than those of HS strips. The grain growth rate of the LS strips during final annealing was faster than that of the HS strips, which may be attributed to the pinning effects of segregated sulfur. With increasing final annealing temperature, B10 value increased rapidly and the saturation level in B10 increased.

• KCI Concrete Journal
• /
• v.11 no.3
• /
• pp.79-88
• /
• 1999

Most difficulties of inducing high fluidity on the concrete mixing design with a strength range of 210 to 240kg/$\textrm{cm}^2$ result from the segregation of aggregates due to the shortage of cementitious binders. To solve the problem, this study concentrated on finding the optimized amount of binder material which does not affect the concrete strength and is also economical. Also there were studies on the use of intermediate sized aggregates to avoid the gap-grading between coarse and fine aggregates so that the material segregation in high flowing concrete was and minimalized the fluidity and penetration capacity of the reinforcing bars was enhanced. Throughout the parametric study with respect to water/binder ratio. superplasticizer. replaceable mineral admixture, the size of coarse aggregate and mixing methods, the effect of each constituent on the characteristics of high flowing concrete could be observed. As a result or partially using stone powder or an intermediate class of aggregate (max. diameter 13mm) . it was fund that the fluidity of concrete significantly increased without material segregation and any change of compressive strengths. It was also proved in this study that proper mixing time and speed are significant factors influence the performence of high flowing concrete.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2000.10a
• /
• pp.178-184
• /
• 2000

To obtain high quality component with thixoforming process, it is important that the homegeneous distribution of solid particles without liquid segregation. In closed-die semi-solid forging process, liquid segregation is strongly affected by injection velocity than any other process variables because the material has to travel relatively long distance to fill the cavity through a narrow gate before solidification begins. The optimal injection velocity and die temperature were investigated to fabricate near-net-shape compressor component called Al frame.