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과공정 Al - Si 합금의 반응고 교반시 초정 Si 형상에 미치는 교반조건 및 개량원소 첨가 영향
김인준,김도향 ( In Joon Kim,Do Hyang Kim ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.5
N/A Microstructural characteristics of semi-solid state processed hypereutectic Al-Si alloys have been investigated. Main concern of the present study is to investigate the effects of P and Sr addition on the size and morphology change of the primary Si particles. Refinement of the primary Si particles was observed with the addition of P and Sr at the early stage of semi-solid state processing, but such a refining effects became negligible resulting in Si particles with a near-spherical morphology with continuous stirring. This implies that the microstructural transformation mechanism became more dependent to stirring effects than to the alloying effects during semi-solid state processing. Brittle fracture and agglomeration were proposed as the mechanisms for microstructural alterations during semi-solid state processing. (Received June 30, 1998)
Al65Cu20Fe15 합금에서 안정한 Icosahedral 준결정상의 형성 거동
이상목,김도향,전형준 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.8
The solidification sequence and the formation of the stable quasicrystalline icosahedral phase were investigated in a conventionally cast Al_(65)Cu_(20)Fe_(15) ingot by the combined analysis of SEM-EDX, TEM, XRD, and DTA. An Al_(65)Cu_(20)Fe_(15) alloy was melted in an inductively heated crucible, and then cast into a liquid nitrogencooled wedge-type steel mold under a dynamic argon atmosphere. Rapidly solidified ribbons were also prepared by single roller melt spinning. The microstructural evolution and the formation of icosahedral phase were examined as a function of heat treatment at the solid-liquid mixed region. Icosahedral phase was observed to form at the boundary of λ-Al_(13)Fe₄ phase via a peritectic reaction, and τ-AlCu(Fe) phase was formed in the remaining liquid. The composition corresponding to ω-Al_7Cu₂Fe was also detected in the area of icosahedral phase. It is suggested that the detailed solidification sequence and the resultant morphology of an Al-Cu-Fe alloy are subject to change as a function of cooling rate during solidification and heat treatment condition.
Al-Mg 합금에서 가스-용탕 in-situ 반응에 의한 AIN의 형성
이명수,신광선,김도향,전형준 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.5
Formation of AlN by means of a melt-gas in-situ reaction in Al-10wt.%Mg and Al-20wt.%Mg alloys has teen investigated. N₂+ 5% H₂ gas was used for AlV formation. Melt-gas in-situ reaction was carried out at 900℃ for 16 and 32hours. Formation of AlN has been identified by a variety of analytic methods : optical, scanning electron, transmission electron microscopies, X-ray diffraction, energy dispersive X-ray spectroscopy and image analyzing technique. AlN particles exist uniformly in the form of clusters mainly at interdendritic area together with the eutectic mixture of α-Al and Al₃Mg₂ The reason for clusters to be formed may be : 1) heterogeneous nucleation on the preexisting AlN particles . 2) reduction of interfacial energy by forming aggregates of particles : or 3) reaction of Al and Mg₃N₂. Individual AlN particle has a shape of a hexagon type thin plate. Amount and size of AlN increased with reaction time. Thickness and width of AlN are approximately 0.3㎛ and 0.9-1.8㎛ respectively after reaction for 16 hours, and approximately 0.3-0.4㎛ and 1.5-2.2㎛ respectively after reaction for 32 hours. AlN/α-Al interface was stable after being exposed at 500℃ Thermodynamic reasoning shows that Mg plays an important role in transferring a nitrogen atom from the gas phase to molten Al by forming intermediate Mg₃N₂ particles which are eventually changed into AlN by reaction with Al melt.
Ca, P 의 첨가가 용탕단조 Mg-Al-Zn-Si 합금의 미세조직에 미치는 영향
박성진,김낙준,김도향,김재중,신철수 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.12
Effects of alloying elements such as Ca and P on the microstructure of squeeze cast Mg-Al-Zn-Si alloys have been investigated in the present study. Addition of Si in Mg-Al-Zn alloys results in the formation of Mg₂Si in two types of morphologies; polygonal type and chinese script type. With increasing Al content the formation of polygonal type Mg₂Si is pronounced. Addition of Ca results in the homogeneous distribution of fine polygonal Mg₂Si particles. Ca is segregated mainly around the secondary phase such as Mg_(17)Al_(12), P provides the nucleation sites for Mg₂Si, results in the homogeneous distribution of the fine polygonal Mg₂Si particles. Accordingly, Ca and P containing Mg-Al-Zn-Si alloys have the much finer microstructure than those with no Ca and P since the fine polygonal Mg₂Si particles restrict the grain growth of Mg alloys during squeeze casting and subsequent heat treatment.