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반고상 온도구역에서 등온유지한 Al-Si , Al-Cu 및 Mg-Al 합금의 고상형상 및 조직의 변화
정운재,김기태,홍준표 ( Woon Jae Jung,Ki Tae Kim,Chun Pyo Hong ) 한국주조공학회 1996 한국주조공학회지 Vol.16 No.6
N/A Variation of shape and size of solid particles and solute redistribution in Mg-9wt.%Al, Al-4.5wt.Cu, and Al-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.
반고상 Al-4.5wt.%Cu 합금의 등온유지 및 압출조건에 따른 미세조직과 유동성변화
정운재,김기태,홍준표 ( Woon Jae Jung,Ki Tae Kim,Chun Pyo Hong ) 한국주조공학회 1996 한국주조공학회지 Vol.16 No.5
N/A Effects of isothermal heat-treatment at the semisolid temperature region, extrusion rate, and mold temperature on microstructure and fluidity of an Al-4.5wt.%Cu alloy were investigated. Microstructural change during isothermal heat-treatment was similar to that of a Mg-9wt.%Al alloy, but different from that of an Al-7wt.%Si alloy. It was found that the solid phases tend to agglomerate with irregular shape, size and distribution, and the solid boundaries didn`t disappear, as was found in a Mg-9wt.%Al alloy. And nonuniform distribution of solid phase and segregation of solute atoms after extrusion were found. Fluidity was found to be much lower than those of Al-7wt.%Si and Mg-9wt.%Al alloys.
정운재,김동옥 ( Woon Jae Jung,Dong Ok Kim ) 한국주조공학회 1983 한국주조공학회지 Vol.3 No.1
In order to determine the feeding distance of aluminiun alloys (Alsi7Mg and AlCu4Ti) bar castings in the sand mold, the distance of the sound castings has been observed by radiograph for various risers, melt treatment, and casting design. Variation of porosity and hardness with the distance from the riser were also measured in order to determine the casting soundness. The results obained were as follows; 1) The modulus of riser should be 1.4 times of the casting`s 2) The maximum distance which can be made sound is greatly dependent on chemical composition and ingate location, and follows the rules given by the formula; a) When the melt flows into the casting first, and the riser afterward, D = 37.7 √T for AlSi7Mg D = 31.2 √T for pure aluminium D ≥ 3 54.8 √T for AlCu4Ti Where T = casting thickness in ㎜ Of this maximum distance, aa√T for AlSi7Mg and 7.5 √T for pure aluminium is made sound by the chilling effect of the casting edge. b) When the melt flows into the casting passing through the riser, 30×30×600㎜ bars can be made sound in all cases 3) Percentage of porosity is higer in AlCu4Ti than AlSi7Mg. And it is increased gradually by moving closer to the riser in case of 30×30×300㎜ bars, but for the 30×30×600㎜ bars it is increased gradually by moving closer to the center of bars. 4) Hardness variation is similar to the tendency of porosity. And it decreased gradually with approaching to the center in case of 30×30×600㎜ bars
AlSi7Mg 합금의 반고상 가압주조조건에 따른 유동성 및 기계적 성질의 변화
정운재,김기태,홍준표 ( Woon Jae Jung,Ki Tae Kim,Chun Pyo Hong ) 한국주조공학회 1996 한국주조공학회지 Vol.16 No.1
N/A Effects of semi-solid process parameters such as mold temperature, holding temperature, holding time, and extrusion rate on microstructures, fluidity, and mechanical properties of AlSi7Mg alloy have been investigated. During isothermal heat treatment at semi-solid temperature region, solid grains coalesced slowly and the grain shape changed to spherical one. Non-uniform distribution of solid phase and segregation of solute were found along the length of the fluidity test specimen. With an increase of the distance, the solid fraction decreased and the Si content increased. The strength was slightly proportional to the solid fraction, when the extrusion rate is fast. On the other hand, the slow extrusion rate caused an inverse tendency.
Cu-Be-Co 합금의 물성에 미치는 열처리 조건의 영향
정운재,경신호,김기태,김종인 ( Woon Jae Jung,Shin Ho Kyoung,Ki Tae Kim,Jong In Kim ) 한국주조공학회 1994 한국주조공학회지 Vol.14 No.3
N/A The effects of solid solution treatment and aging in the properties of Cu-0.32wt%Be-1.35wt%Co alloy was gravity die casted and forged were investigated in order to examine the optimum heat treatment conditions for production of high conductivity mold material. The optimum properties for mold material were obtained under the conditions which were solid solution treated at 930℃ for 1 hour and aged at 430℃ for 2hours.
알루미늄청동의 합금성분 및 냉각속도에 따른 특성변화에 관한 연구
정운재,김헌주,김동옥,윤의박 ( Woon Jae Jung,Heon Joo Kim,Dong Ok Kim,Eui Pak Yoon ) 한국주조공학회 1988 한국주조공학회지 Vol.8 No.3
N/A Al-bronze has a good mechanical property, corrosion resistance and castability, so being highlighted for the new copper alloy. So, effects of alloy composition and cooling rate in the mechaincal properties and solidification behavior have been investigated. The results obtained are as follows: 1) Change in volume on solidification is larger in metal mold casting than in sand mold casting. And it decreases by the addition of Al. 2) The mechanical property in metal mold casting is superior to the one in sand mold casting, and the inclination is obvious up to 9% Al, after heat-treatment (885℃, 1.5hrs → W·Q → 540℃, 3hrs) 3) By adding Al, the mechanical property is slightly increased up to 9 % Al. Above 9 % Al, it is increased rapidly, and is accelerated by adding Fe. 4) Cooling rate and hardness, and grain size and cooling rate are related as follows in the range of 1100℃ to 1200℃ pouring temperature. Grain size(㎛)=929.6422×cooling rate(℃/sec)^(-0.51537) Hardness(BHN)=765.45713×grain size(㎛)^(-0.31058)
Mg 합금의 반용융가압주조시 주조조건에 의한 금형충전성 및 유동성 변화
정운재,김기태,홍준표 ( Woon Jae Jung,Ki Tae Kim,Chun Pyo Hong ) 한국주조공학회 1995 한국주조공학회지 Vol.15 No.2
N/A Effects of process parameters during thixocasting, such as solid volume fraction, mold temperature and extrusion ratio, on the mold filling behaviour and fluidity of Mg alloy(AZ91D) have been investigated. The semi-solid ingot held for 60 minutes at the semi-solid temperature range did not contain the equilibrium volume fraction of solid as expected from the phase diagram. Therefore, in order to obtain the desired solid fractions, and to suppress the exaggerated grain growth during heating, it was required to heat the ingot rapidly up to the temperature 10℃ higher than the semi-solid temperature suggested from the phase diagram for a specific volume fraction of solid. The experimental results show that mold filling behaviour and fluidity can be improved with the use of the higher mold temperature and the lower volume fraction of solid, but remain nearly unaffected by the change of extrusion ratio.
김헌주,정운재 ( Heon Joo Kim,Woon Jae Jung ) 한국주조공학회 1993 한국주조공학회지 Vol.13 No.6
N/A The wear resistance of Hyper-eutectic Al-Si alloy, have recently been noticed as a new automobile material, was investigated. For the purpose of developing wear resistant Al-Si alloy, some factors which attribute to wear resistance are examined as follows; refinement of primary Si particle during solidification, and effect of refinement on wear resistance and other mechanical properties. The most effective refinement was accomplished by adding both NaF and S, and this improve wear-resistance in abrasive wear type. The wear losses of specimens cast in metal mold were ruduced to 80% of those in sand mold. T6 heat treatment increases hardness, which resulted in reduction of wear loss about 3∼18 %.
Cu-Ag 합금의 전기전도도와 기계적 특성에 미치는 P , Mg 의 영향
정봉용,김기태,정운재,김명호 ( Bong Yong Jeong,Ki Tae Kim,Woon Jae Jung,Myung Ho Kim ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.2
N/A Effects of P and Mg on the electrical conductivity and mechanical properties of Cu-Ag alloys were investigated experimentally. Small addition of these alloying elements decreased the electrical conductivity of Cu alloy greatly, especially for P addition. The maximum amounts of P addition to obtain the electrical conductivity being over 90%IACS was found to be about 0.019wt.%, and in this case recrystallization temperature of the addition was about 450˚C. The tensile strength was not changed significantly by the addition of P. However, for Cu-Ag-P-Mg alloys, P-Mg compound was precipitated by heat treatment at 450˚C for 1 hour. Such a precipitation of P-Mg compound increased the electrical conductivity of the alloy from 47~57%IACS to 72.3~86.6%IACS. (Received January 15, 1998)