Prediction of Microshrinkage Porosity in Thin Al-alloy Permanent Mold Castings

( Zin Hyoung Lee ) 한국주조공학회 1991 한국주조공학회지 Vol.11 No.1

N/A The proper feeding conditions for thin Al-Alloy (AA336, JIS ACB`A) castings in permanent mold were investigated to eliminate microshrinkage porosity. 5mm-thick plates (200mm long, 60mm wide) were cast with increasing padding taper from 0 to 5% under different conditions (1) constant mold temperature of 350℃, (2) continuous production with uniform mold thickness (10㎜), (3) continuous production with a negative taper of 2.5% in mold thickness (thickness decreasing in direction to riser). The test casting were machined off to the midplane and the shrinkage porosity was examined visually. The critical padding taper which can just eliminate the shrinkage porosity was determined for each condition, i.e. : (1) 4.5% at the constant mold temperature, (2) 3.5% for continuous production with the uniform mold thickness (3) 1.5% for continuous production with the taper in mold thickness. A computer simulation by a finite difference analysis program was applied to the test casting. The liquid fraction gradient (LFG) and the temperature gradient divided by the square root of the cooling rate (G /SR) were calculated at the end of solidification and compared with the shrinkage porosity area in the castings. For the case of constant mold temperature, LFG is a better parameter to predict shrinkage porosity than G /SR and its critical value is around 11%/㎝. But for the case of continuous production, neither LFG nor G /SR could be a reliable parameter. The experimental results about the critical padding taper are of practical interest for designing permanent molds and castings. The computer simulation results stimulate further research to be directed on the prediction of centerline microshrinkage porosity in continuous production.

Present Situation of Education and Research on Foundry Engineering on Korea

Lee,Zin Hyoung 한국주조공학회 2001 한국주조공학회지 Vol.21 No.4

Effects of High Temperature Annealing on the Chemical Homogeneity and Magnetostriction of Tb0.3Dy0.7Fe1.90 Intermetallic Compound

Lee, Zin Hyoung,Kim, Jong Chul,Park, Won Je,Ye, Byung Joon,Son, Dae Rak 대한금속재료학회(대한금속학회) 1998 METALS AND MATERIALS International Vol.4 No.6

A rare earth-iron intermetallic compound Tb_(0.3)Dy_(0.7)Fe_(1.90), also called Terfenol-D, has a gigantic room temperature magnetostriction at a relatively small magnetic field. In this study microsegregation of Tb and Dy in directionally solidified Terfenol-D was investigated. It was predicted from a calculated phase diagram and experimentally verified that Tb concentration at the center of the cell which solidified earlier was lower than that at the cell boundary. In order to homogenize this microsegregation, specimens were annealed at 1000℃ for 40 hours, and various magnetic properties were measured as a function of applied field under uniaxial compressive stress in the range from 0.5 to l.2 MPa. After the annealing, the maximum magnetostriction increased at a compressive stress below 9 MPa, magnetostrictive coefficient d_(33) and magneto-elastic coupling coefficient k_(33) increased, but permeability decreased. These results may be due to the reduction of magnetocrystalline energy which was locally very high before annealing due to microsegregation.

Al 합금용탕의 (合金熔湯) C2Cl6 정제-탈가스에 의한 Mg 의 손실

이진형 ( Zin Hyoung Lee ) 한국주조공학회 1981 한국주조공학회지 Vol.1 No.3

N/A The Mg-loss of AlSi 7% melts containing from 0 to 0.8% Mg during the Hexachloroethane tablet degassing was investigated. The results of the experiment was discussed in view of the free energy change and kinetics of MgCl₂formation. The melts with Mg content less than 0.5% showed a Mg-loss proportional to Mg-content, while it was constant at about 24% of the weight of tablets, when Mg content of the melt became more than 0.5 %. The rate of Mg-loss was drastically reduced, when the amount of tablets used at a time increased ver a certain limit for a given melt quantity.

T5 열처리한 Al 합금 금형주조품에서 경도의 역분포현상

이진형 ( Zin Hyoung Lee ) 한국주조공학회 1988 한국주조공학회지 Vol.8 No.3

N/A Aluminum alloy permanent mold castings often exhibit in as-cast or T5-heat treated state an inverse distribution of hardness, i,e. thinner sections have lower hardness than thicker sections. This phenomina is explained by measuring the cooling curves in a test casting in an Aluminum piston alloy (AC8A or A332). Thinner sections solidify- faster but later cooles down more slowly than thicker sections in temperature range where coarse precipitation of supersaturated elements can take place. The precipitation rate of Mg₂Si phase in A332 alloy seems to be maximum at around 490℃.

다결정 Si 기판의 진공주조법에 관한 연구

이진형,이근희 한국주조공학회 2000 한국주조공학회지 Vol.20 No.3

A vacuum casting was proposed as a new fabrication method of Si wafer for solar cell substrate. It was tried to fabricate a Si plate with good properties and to reduce the production cost by direct vacuum casting. By 5-10㎝Hg of pressure difference Si plate with 50×46×1.5㎣ was fabricated. For the preventing of the reaction between graphite mold and Si melt, BN powder coating or BN insert were used. The Si wafer was poly crystalline with 100㎛∼1㎜ order of grain size. And there were some twins and dislocations in the grains.

치과 주조용 Ag-Pd 계 합금의 미세조직에 미치는 S 와 Ir 의 영향

이진형,서용찬,신승렬 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.1

The effects of S and Ir on the microstructures of binary Ag-25%Pd alloy and a commercial alloy, A-2 (Ag-25 wt%Pd-2 wt%Au-2 wt%In-0.84 wt%Zn-0.5 wt%Ir) were studied. The segregation tendency of S in the grain boundary was investigated by Auger electron spectroscopy (AES) and Energy Dispersive Spectroscopy (EDS) with varying S concentrations. The effect of the cooling rate on the microstructures and segregation was also investigated. The compositions of several positions on the fractured surface were measured by EDS analysis. The grain refining effect of Ir was obvious when the concentration of Ir was more than 0.1%. At S-concentrations above 0.1%, Ag₂Pd₃S phase was observed at the dendrite and grain boundary due to S-segregation during solidification. This phase did not appear at 0.01% S, but the S-concentration at the grain boundary was much higher than the bulk concentration, showing S-segregation to the grain boundary. The degree of S-segregation to the grain boundary decreased slightly with grain refining. The segregation of In and Zn in A-2 alloy containing high S concentration did not occur while it occurred in the alloy with low S concentration.

가스분무된 알루미늄 합금분말의 탈가스에 관한 연구

이진형,서용찬,조대식 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.7

In RS aluminum alloy powders, the surface oxide formed on powders usually contains significant amounts of physically adsorbed water and oxygen. Hence, it is necessary to remove both the adsorbed gas and water from the surface of the powders before consolidation, in order to achieve full density. This removal is usually accomplished by a degassing step. A study has been perfomed on the effectiveness of degassing processes of AC8A alloy powders. Mathematical analysis on the degassing time in the degassing process was done and the factors determining the degassing time were investigated. Computer simulation for degassing process in the powder compact was done considering evaporation, diffusion and reaction. According to the results of simulation, degassing time decreases with decreasing size of powder compact and increasing pore radius. Based on the above results, two method of degassing was performed and compared: static degassing process and dynamic degassing process. The mechanical properties of the specimen made from the dynamic degassing method was superior and its degassing time was much shorter than the other method.

AlSi7Mg 용탕의 C2Cl6 정제 탈가스효과에 미치는 Mg 의 영향

이진형,정운재 대한금속재료학회(대한금속학회) 1982 대한금속·재료학회지 Vol.20 No.4

The degassing of Al melts, an essential part of Al foundry practice, has often an unpredictable result, as the effects of many factors are not well known. The effects of Mg content, initial gas content, amount of degassing tablets and moisture content of the air on C₂Cl_6 - tablet degassing of AlSi7Mg melt were investigated. The degassing efficiency decreases rapidly with increasing Mg content up to 0.1% and then remains constant. And it becomes gradually worse when the amount of degassing tablets for one plunging increases. The experimental results were analyzed statistically and an equation, C₂=C₁exp(-kd), was formulated, to calculate the gas content C, after a degassing treatment with C₂Cl_6-tablet d, where k is a function of Mg content.

A study on the fabrication of poly crystalline Si wafer by vacuum casting method and the measurement of the efficiency of solar cell

Lee, Geun-Hee,Lee, Zin-Hyoung The Korea Association of Crystal Growth 2002 韓國結晶成長學會誌 Vol.12 No.3

Si-wafers for solar cells were cast in a size of $50{\times}46{\times}0.5{\textrm}{mm}^3$ by vacuum casting method. The graphite mold coated by BN powder, which was to prevent the reaction of carbon with the molten silicon, was used. Without coating, the wetting and reaction of Si melt to graphite mold was very severe. In the case of BN coating, SiC was formed in the shape of tiny islands at the surface of Si wafer by the reaction between Si-melt and carbon of the graphite mold on the high temperature. The grain size was about 1 mm. The efficiency of Si solar cell was lower than that of Si solar cell fabricated on commercial single and poly crystalline Si wafer. The reason of low efficiency was discussed.