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용탕단조한 과공정 Al-Si 합금(A390)의 미세조직과 기계적 성질
주대헌,신희택,김명호 ( Dae Heon Joo,Hee Teak Shin,Myung Ho Kim ) 한국주조공학회 1996 한국주조공학회지 Vol.16 No.1
N/A The effects of squeeze casting process on the microstructure and mechanical properties of hypereutectic Al-Si alloy have been studied. The effect of T6 heat treatment has also been examined. The mold for indirect squeeze casting was designed to fabricate 15ø and 25ø specimens and the 50ø specimen was fabricated by direct squeeze casting. The measured cooling rates during solidification of 50ø, 25ø and 15ø specimens are about 36℃ /sec., 88℃/sec. and 106℃/sec., respectively. There were no clear difference in size and distribution of primary Si particles of the A390 alloy modified at 850℃ with P(Cu-P) additions in 15ø and 25ø, 50ø squeeze cast specimens. However, the size and distribution of primary Si particles of the A390 alloy modified at 800℃ were found to be affected by cooling rates during solidification. A further important observation was that eutectic structure was greatly refined by pressure application during solidification and the eutectic Si of 15ø specimen was finer than that of 25ø and 50ø specimens. Due to the microstructural refinement, mechanical properties of 15ø specimen were found to be better than those of 25ø and 50ø ones. After T6 heat treatment, the mechanical properties were remarkably improved.
용탕단조한 Ni-aluminide 보강 AC8A 기 복합재료의 조직 및 특성
주대헌,김명호,권숙인,김준수 ( Dae Heon Joo,Myung Ho Kim,Suk In Kwun,Jun Su Kim ) 한국주조공학회 1997 한국주조공학회지 Vol.17 No.2
N/A AC8A matrix composites reinforced with Ni-aluminide were fabricated by squeeze casting process, and the characteristics and nature of the growth of Ni-aluminide phases at the interface between nickel and aluminum were investigated. In the as-cast composites, the reaction layer between Ni skeleton and aluminum matrix was found to be NiAl₃, regardless of the casting temperatures and the kinds of preforms. During high temperature solution treatment the NiAl₃, layer grew and formed new Ni₂Al₃ layer. Because of presence of the porosity formed by Kirkendall effect at the interface between NiAl₃, and aluminum matrix, the tensile strength of composites was inferior to that of AC8A matrix alloy. However, the composites exhibited superior wear resistance due to the formation Ni-aluminide intermetallic phases. Composite A, of which Ni skeleton was fully transformed into Ni-aluminide, shows better wear resistance than that of composite B which still possessed some unreacted Ni skeleton.
BcuP 계 합금의 쌍롤주조시 주조특성과 미세조직에 미치는 주입온도의 영향
주대헌(Dae Heon Joo),김명호(Myung Ho Kim) 한국주조공학회 2001 한국주조공학회지 Vol.21 No.4
N/A Experimental study on the twin roll strip casting of BCuP-5(Cu-15wt%Ag-wt5%P) alloy was carried out using laboratory scale horizontal type twin roll caster. In this study, among the various operating parameters, such as tundish angle, contact angle, pouring temperature, roll speed, presetting gap of the rolls and kinds of roll and tundish materials, effect of pouring temperature for strip casting of BCuP-5 alloy which has long freezing range of about 170℃ was mainly investigated. BCuP-5 alloy strip was successfully produced when pouring molten metal at lower temperature than its liquidus temperature. Microstructure of the cast strip consists of primary Cu and eutectic. Especially the size of primary Cu phase increased with decreasing of pouring temperature.
용탕압출법에 의한 Al-Cu 합금 선재의 제조에 관한 연구
주대헌 ( Dae Heon Joo ),이병수 ( Byoung Soo Lee ),김명호 ( Myung Ho Kim ) 한국주조공학회 2004 한국주조공학회지 Vol.24 No.6
N/A Melt-extrusion process, a metallic melt poured and solidified up to semisolid state in the container can be directly extruded through the die exit to form a product of bar shape without other intermediate processes. In this study, the fabrication characteristics of the process were evaluated with various process parameters, such as preheating temperature of extrusion dies, extrusion temperature and extrusion ratio. Al-Cu alloys were successfully extruded after squeezing out of liquid during melt-extrusion with smaller force compared to the solid extrusion. Soundly Al-Cu alloy bar was fabricated at the preheating temperature of 500-520℃. The range of extrusion temperature for soundly melt-extruded Al-Cu alloy bar was increased with increasing extrusion ratio. Mechanical properties of melt-extruded Al-Cu alloy bars were found change with Cu content of the melt-extruded bars due to the occurrence of segregation. The various extrusion temperature yielded equiaxed structure with a grains size about 200 ㎛.
주대헌(Dae Heon Joo),박주승(Joo Seung Park),김명호(Myung Ho Kim) 한국주조공학회 2001 한국주조공학회지 Vol.21 No.3
N/A In determining properties of ductile cast iron, it is well known that nodularity plays a significant role. Therefore, the national and/or international standards for ductile cast iron such as KS, ISO, ASTM and JIS have specified some methods for evaluating it. However, most of standards have not recommended the methods using image analyzer which is known as an objective analyzing tool for evaluating microstructure. In this study, a reliable method for evaluating nodularity by image analyzing method was proposed, and the result was compared with that from the common counting method proposed in KS D 4302-1999. It was found that there was a reasonable relationship in nodularities measured by these two methods.
Al-Sn 합금의 마찰 특성에 미치는 Sn 형상의 영향
李定根,朱大憲,金文鉉,金明鎬 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.10
Effects of Sn morphology on the friction and wear characteristics of Al-Sn alloys were investigated by using the tribology tester, optical microscope and scanning electron microscope. Three different types of Sn morphologies named elongated, small network and large network structure were obtained by cladding and heat treatment. Wear resistance of the specimen having large network structure exhibited better anti-friction characteristics compare to that of the elongated structure. Also specific wear rate and friction coefficient decreased markedly with change of Sn morphology from elongated to large network structure. Abrasive and adhesive wear occurred for the elongated structure, while oxidation wear was observed for the network structure.
정봉용,주대헌,박주승,김명호 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.9
This paper reports an investigation of the characteristics of plasma duplex treated ductile cast irons during thermal fatigue tests on a thermal cycling rig. The thermal fatigue cracking behaviors and microstructure of untreated and plasma surface treated ductile cast irons have been investigated. Both ferrite and pearlite matrix ductile cast irons were evaluated. During the tests, 60 mm long cylinders with 20 mm diameter were subjected to 1,000 high frequency induction heating and water cooling cycles, lasting 7 and 5 sec, respectively. The thermal fatigue damage was evaluated by analyzing different crack dimensions and distribution by light microscopy. The results showed that the plasma surface treatment increased thermal fatigue cracking resistance. When thermal fatigue cracking occurs, the cracks always initiate at the surface of the specimen. The major path of crack propagation is generally along the ferrite grain boundaries. The hardened layer had an effect on the thermal fatigue property. In addition, the ductile cast iron with an pearlite matrix has a better resistance to thermal fatigue than that of ferrite matrix.
과공정 Al-Si 합금의 열팽창 특성에 미치는 Si 입자 크기의 영향
김철현 ( Kim Cheol Hyeon ),주대헌 ( Ju Dae Heon ),김명호 ( Kim Myeong Ho ),윤의박 ( Yun Ui Bag ),윤우영 ( Yun U Yeong ),김권희 ( Kim Gwon Hui ) 한국주조공학회 2003 한국주조공학회지 Vol.23 No.4
N/A Hyper-eutectic Al-Si alloy is used much to automatic parts and material for the electronic parts because of the low coefficient of thermal expansion, superior thermal stability and superior wear resistance. In this work, A390 alloy specimens were fabricated for control of the Si particle size by various processes, such as spray-casting, permanent mold-casting and squeeze-casting. To minimize the effect of microporosity of the specimen, hot extrusion was carried out under equal condition. Each specimens were evaluated tensile properties at room temperature and thermal expansion properties in the range from room temperature to 400℃. Ultimate tensile strength and elongation of the spray-cast and extruded specimens which have fine and well distributed Si particles were improved greatly compare to the permanent mold-cast and extruded ones. Specimens which have finer Si particles showed higher ultimate tensile strength and elongation than those having large Si particle size, and coefficient of thermal expansion of the specimens increased linearly with Si particle size. In case of the repeated high temperature exposures, thermal expansion properties of the spray-cast and extruded specimens were found to be more stable than those of the others due to the effect of fine and well distributed Si particles.