• Metals and materials international
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• v.24 no.6
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• pp.1376-1385
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• 2018

Ultrasonic melt treatment (UST) was applied to an A390 hypereutectic Al-Si alloy in a temperature range of $750-800^{\circ}C$ and its influence on the solidification structure and the consequent increase in strength was investigated. UST at such a high temperature, which is about $100^{\circ}C$ above the liquidus temperature, had little effect on the grain refinement but enhanced the homogeneity of the microstructure with the uniform distribution of constituent phases (e.g. primary Si, ${\alpha}-Al$ and intermetallics) significantly refined. With the microstructural homogeneity, quantitative analysis confirmed that UST was found to suppress the formation of Cu-bearing phases, i.e., $Q-Al_5Cu_2Mg_8Si_6$, $Al_2Cu$ phases that form in the final stage of solidification while notably increasing the average Cu contents in the matrix from 1.29 to 2.06 wt%. A tensile test exhibits an increase in the yield strength of the as-cast alloy from 185 to 208 MPa, which is mainly associated with the solute increment within the matrix. The important role of UST in the microstructure evolution during solidification is discussed and the mechanism covering the microstructure-strengthening interrelationship of the ultrasonically treated A390 alloy is proposed.

• Korean Journal of Metals and Materials
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• v.49 no.1
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• pp.58-63
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• 2011

The grain size and growth direction of a directionally solidified turbine blade were evaluated by the initial nucleation condition at the start block of directional solidification. The initial nucleation condition was controlled by inserting a Ni foil on the directional solidification plate of the directional solidification furnace. Fine grains with good orientation were obtained in the faster cooling condition at the start block. The nucleus number was compared with the cooling rate of the start block by electron back scattered diffraction (EBSD). DSC (differential scanning calorimeter) analysis was performed to compare the melting point and undercooling for nucleation of the coarse nuclei and fine nuclei of the start block. The faster cooling condition at the start block showed more undercooling for nucleation and smaller size of nuclei which resulted in a fine grain with good orientation in the directional turbine blade.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.2
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• pp.808-816
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• 2012

This paper is the study for the directional solidification of the ingot through the thermal analysis simulation and structural change of casting furnace. With the results of thermal analysis simulation, the silicon as a whole has reached the melting temperature as the retention time 80 min. The best cooling conditions showed at the upper cooling temperature $1,400^{\circ}C$ and cooling time 60min. The fabricated wafers showed the superior etching result at the grain boundary than that of existing commercial wafers. The FTIR measurements of oxygen and carbon impurities were not in the critical value for solar conversion efficiency. The NAA analysis of metal impurities were also detected the total number of 18 different metals, but the concentration distribution showed no significant positional deviations in the same position from the top to the bottom.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.4
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• pp.1915-1920
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• 2013

This paper is the study for the directional solidification of the ingot through the thermal analysis simulation and structural change of casting furnace. With the results of thermal analysis simulation, the silicon as a whole has reached the melting temperature as the retention time 80 min. The best cooling conditions showed at the upper cooling temperature $1,400^{\circ}C$ and cooling time 60min. The fabricated wafers showed the superior etching result at the grain boundary than that of existing commercial wafers. The FTIR measurements of oxygen and carbon impurities were not in the critical value for solar conversion efficiency. The NAA analysis of metal impurities were also detected the total number of 18 different metals, but the concentration distribution showed no significant positional deviations in the same position from the top to the bottom.

• Korean Journal of Materials Research
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• v.32 no.9
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• pp.391-395
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• 2022

Research is being actively conducted on the continuous thin plate casting method, which is used to manufacture magnesium alloy plate for plastic processing. This study applied a heat transfer solidification analysis method to the melt drag process. The heat transfer coefficient between the molten magnesium alloy metal and the roll in the thin plate manufacturing process using the melt drag method has not been clearly established until now, and the results were used to determine the temperature change. The estimated heat transfer coefficient for a roll speed of 30 m/min was 1.33 × 10⁵ W/m²·K, which was very large compared to the heat transfer coefficient used in the solidification analysis of general aluminum castings. The heat transfer coefficient between the molten metal and the roll estimated in the range of the roll speed of 5 to 90 m/min was 1.42 × 10⁵ to 8.95 × 10⁴ W/m²·K. The cooling rate was calculated using a method based on the results of deriving the temperature change of the molten metal and the roll, using the estimated heat transfer coefficient. The DAS was estimated from the relationship between the cooling rate and DAS, and compared with the experimental value. When the magnesium alloy is manufactured by the melt drag method, the cooling rate of the thin plate is in the range of about 1.4 × 10³ to 1.0 × 10⁴ K/s.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.06a
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• pp.621-622
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• 2007

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.1
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• pp.193-201
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• 1995

The role of thermal contact resistance between a casting and a metal mold as well as natural convection in the melt during solidification of a pure metal is numerically studied. Numerical simulation is performed for a rectangular cavity using the coordinate transformation by boundary-fitted coordinate and pure aluminum is used as the phase- change material. The influences of thermal contact resistance on the interface shape and position, solidified volume fraction, temperature field and local heat transfer are investigated.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2004.02a
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• pp.28-41
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• 2004

The study is aimed to assess the usefulness of the mixture design for spent resin immobilization in cement. Although a considerable amount of research has been carried out to determine the limits for the composition of an acceptable resin-cement mixture, no efficient experimental strategy exists that explores the full properties of waste form against composition relationship. In order to gain an overall view, this report introduces the method of mixture design and mixture analysis, and describes the design of experiment of the 5-component mixture with the constraint conditions. The mathematic models of 28-day compressive strength varying with the ingredients are fitted, and the main effect and interaction effect of two ingredients are identified quantitatively along with the graphical interpretation using the response trace plot and contour plots.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1364-1367
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• 1996

Recently, direct rolling process, called as strip casting process, has been interested in to save production cost by reducing forming processes. In direct rolling process, since a steel strip of thickness 1-5(mm) can be produced directly from molten metal, it can eliminate secondary hot rolling process. On the other hand, since many process variables are existed in this process and relation of these variables is very complex, it is difficult to realize the process design and the quality control. In this paper, as first step to overcome above difficulties, the quantitative relationship of the process variables affected to quality of the strip has been carried out through the numerical analysis. Also, we determined the process variable to monitor the quality in the direct rolling process. As a result, we show that the solidification final point, called as Nip point, was related directly to quality of the strip.

• 연구논문집
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• s.29
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• pp.173-183
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• 1999

The vacuum investment casting process for a large gas turbine component, Inner Preswirl Support (IPS), was simulated by using commercial FEM package ProCAST(TM) with view factor radiation method. The solid fraction in mushy zone was directly measured by Differential thermal analysis(DTA-DSC mode). Three types gating design. considering liquid flow and heat release through it. were proposed. Solidification had begun at the ribs or thin sections of the IPS casting and advanced further through the upper and lower gates. The computed temperature gradient G and G/R values at 70% solidified temperature were used for prediction of microshrinkage formation during casting. The effect of mold preheat on the thermal history of the casting displayed minute effect on the microshrinkage formation.