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Sc첨가한 Al-Mg 합금의 고온변형 거동에 미치는 결정립 크기의 영향
우기도,김석원,김학신,양창호,박희찬,박경태,Woo, K.D.,Kim, S.W.,Kim, H.S.,Yang, C.H.,Park, H.C.,MIURA, Y.,Park, K.T. 한국재료학회 2002 한국재료학회지 Vol.12 No.9
High temperature tensile test has been performed at $450^{\circ}C$ at different strain rate with various grain size due to different reduction rate of Al-4wt%Mg-0.4wt%Sc alloy which is known to be one of useful superplastic alloys. The grain size of Al-4wt%Mg-0.4wt%Sc alloy is $67~100\mu\textrm{m}$ which is courser than that of the alloy which is commonly used as the superplastic material. The total elongation of the Al-4wt%Mg-0.4wt%Sc alloy is strongly dependent on the average grain size, and is a linear function of the inverse average grain size for the present alloy.
우기도,박영구,김석원,진영철,류재화,나종필 ( K . D . Woo,Y . K . Park,K . W . Kim,Y . C . Jin,J . H . Ryu,J . P . Ra ) 한국열처리공학회 1998 熱處理工學會誌 Vol.11 No.2
N/A The graphitization is affected by the addition of small amount of the elements, such as Si, Al, Ni, B, Cr and Mn etc. Boron is well known as the most effective element for the graphitization of cementite in high carbon steels. But a study on quantitative analysis of B effect on the graphitization is few reported. Therefore the effect of boron addition in Fe-0.65%C-1.0%Si-0.5%Mn steels on the graphitization is investigated quantitatively using hardness tester, optical microscope and scanning electron microscope, neutron induced microscopic radiography. The graphitization in high carbon steels is promoted with 0.003∼0.005%B addition. But the graphitization in steels which has no boron takes long holding time at 680∼720℃. The hardness of quenched steel containing 0.003%B is higher than that of 0.005%B added steel due to complete dissolution of fine graphites into the austenite. The 0.003%B added high carbon steel graphitized at 680℃ for 25hr is useful steel for the agricultural implements and automobile parts which needed a good formability and high hardness.
Al-Li-(Cu , Zr) 합금에서 시효에 따른 δ' 상의 형상 및 입자크기분포의 변화
우기도,조현기 ( K . D . Woo,H . K . Cho ) 한국열처리공학회 1994 熱處理工學會誌 Vol.7 No.2
The present work was aimed to examine the changes of the shape and particle size distribution(PSD) of δ` particles on ageing in Al-Li-(Cu, Zr) alloys which had low density, high specific strength and stiffness. Increasing ageing time and temperature resulted in particles whose aspect ratio tended toward 1. The aspect ratio of δ` particles was not dependent upon the ageing temperature and time in Al-Li-Cu alloy but was dependent upon them in Al-Li-Zr alloy. The PSD of δ` particles in Al-Li-Zr alloy skewed to the right hand compared with that in Al-Li-Cu alloy, because Al₃Zr phase in Al-Li-Zr alloy formed before ageing promoted the precipitation and growth of δ` phase. Therefore, the PSD of the δ` particles was found to be affected by the presence of Al₃Zr particles. The growth rate of δ` phase was not affected by the existence of the third transition phase T₁formed by the addition of Cu in Al-Li alloy but was affected by the existence of Al₃Zr formed by the addition of Zr in Al-Li alloy.
ADI 의 탄성계수와 내마모성에 미치는 합금원소 및 열처리 영향
김석원,우기도,진영철 ( S . W . Kim,K . D . Woo,Y . C . Jin ) 한국열처리공학회 1998 熱處理工學會誌 Vol.11 No.2
N/A The elastic modulus and wear resistance in austempered ductile cast iron(ADI) are two important mechanical properties for automobile parts. Therefore, the effect of Cu, Ni, Mo and special austempering treatment such as preheated, prequenched, and step austempering treatments on elastic modulus and wear resistance has been investigated systomatically. As a result, elastic modulus and wear resistance were increased by the addition of Mo-Cu and preheated austempering treatment.
송기호,정동석,우기도 ( K . H . Song,T . S . Cheong,K . D . Woo ) 한국열처리공학회 1992 熱處理工學會誌 Vol.5 No.4
A study of the precipitation process of Al-Li binary alloy at low ageing temperature has been carried by electrical resistivity measurement. Two types of G.P. zones were formed during ageing at low temperature. G.P.(1) zone and G.P.(2) zone have been formed primarily at ageing temperature below 60℃ and at ageing temperature range of 80℃ to 100℃, respectively. Therefore the precipitation process of Al-Li binary alloy was as follows ; G.P.(1) zone→G.P.(2) zone→δ`→δ G.P.(1) zone might be affected by excess vacancies, but G.P.(2) zone might be affected by secondary defects, clusters and Li-vacancy pairs. The activation energy for formation of G.P.(2) zone is 0.87eV. It is lower than that of Al-Cu alloy.
Cu , Mg을 함유한 Al-Li 합금의 기계적 성질과 전기저항 변화에 미치는 기본 및 추가 강화상들의 역할
정동석,송기호,우기도 ( D . S . Chung,K . H . Song,K . D . Woo ) 한국열처리공학회 1994 熱處理工學會誌 Vol.7 No.2
Roles of fundamental and additional hardening precipitates on the changes of mechanical properties and electrical resistivity during precipitation decomposition in binary Al-Li, ternaty Al-Lieu and multi-Li-Cu-Mg-Zr alloys have been investigated by the detailed measurement of electrical resistivity, hardness and tensile strength and the observation of transmission electron micrographs. Peek hardness and tensile strength in multi-component Al-Lieu-Mg-Zr Alloy had higher than that of the other alloys and the results of measurement of hardness, strength and electrical resistivity in each alloys aged at 90 and 190℃ precipitation behaviors and mechanical properties in binary, ternary and multi component Al-Li alloys were contributed to the δ`, precursory phase of δ`, T₁, G.P.B. zone and S`phases, respectively.
자동차 부품용 내열, 고온 내산화성 고Si 구상흑연주철의 제조기술개발
김석원(S. W. Kim),우기도(K. D. Woo),한상원(S. W. Han),김정규(J. K. Kim) 한국자동차공학회 1996 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1996 No.6_1
The study aims to compare the characteristics of high temperature oxidation in various High Si Ductile Cast Iron (HSOCI) in order to improve the material for exhaust manifolds which require stronger heat resistance. The specimens containing 2~6% Si and 0~4%Mo were heated in 650℃~950℃ for 100hrs, and 650℃ for 5~20 day. Consequently, amount of oxidation were decreased<br/> with increase of Si, Mo, due to the formation of Fe₂SiO₄and Mo carbide. As the amount of Si and Mo increase, hardness is increased but charpy impact energy in deceased. This is because that the Si solution and Mo carbide in matrix increase with increase of Si, Mo. As a result of addition of various alloy elements in the cast iron which contained 3.5%C, anti-oxidation property is improved, but toughness is decreased with increase of Si, Mo