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내산화성 Mg 모합금을 이용한 고(高) Mg 함유 ECO-Almag6~9 합금 압출재의 제조 및 특성평가
김봉환 ( Bong-hwan Kim ),윤영옥 ( Young-Ok Yoon ),김세광 ( Shae-Kwang Kim ) 한국주조공학회 2021 한국주조공학회지 Vol.41 No.3
산업용으로 활용되는 많은 알루미늄 합금에 마그네슘 성분이 포함되어 있다. 이들 알루미늄 합금에 첨가된 마그네슘 원소는 알루미늄의 강도를 향상시키는 역할을 하지만, 제조 과정 중 산화 경향이 크기 때문에 제품의 품질과 특성을 저해하는 원인이 된다. 마그네슘이 주요 합금원소인 5천계 알루미늄 전신재 합금의 경우, 높은 산화성으로 인하여 마그네슘 함량은 약 5wt% 이내에서만 활용된다. 본 연구에서는 산화 경향이 억제된 것으로 알려진 ECO-Mg 모합금을 이용하여 5wt% 이상의 높은 마그네슘 함량을 포함하는 새로운 합금, ECO-Amag6~9 (6~9wt%Mg 함유) 합금을 제조하고 그 특성을 평가하였다. ECO-Almag6~9 합금은 높은 Mg 함량에도 깨끗한 용탕 품질이 확보되어 양산용 DC 주조기를 이용한 빌렛 제조 및 압출이 가능하였다. 또한 높은 Mg 함량으로 인해기존 산업용 5xxx계 합금에 비해 높은 강도와 연성을 보여 산업적 활용성이 높을 것으로 기대된다. The magnesium is one of the important alloying elements in the conventional aluminum alloys. The addition of magnesium to aluminum is well known to increase the mechanical strength of the aluminum without the trade-off of the decreased elongation. However, the content of magnesium in aluminum alloys has been limited to be lower than about 5wt.% because of the high oxidation tendency of magnesium element during the manufacturing processes such as casting, hot-forming and post heat-treatments, which can deteriorate the quality and properties of the final products. In this study, new ‘ECO-Almag6~9’ (containing 6~9wt%Mg) alloys were investigated to be made of the ECO-Mg master alloy, which has been invented to reduce the oxidation tendency of itself. It was successfully demonstrated that ECO-Almag6~9 alloys can be fabricated through the mass-production facilities of DC casting and extrusion routes without the problems of magnesium oxidation. In addition, it was confirmed that the strength and ductility were simultaneously improved due to the addition of high magnesium contents.
박순용 ( Soon Yong Park ),김세광 ( Shae Kwang Kim ),이동복 ( Dong Bok Lee ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.6
CaO-added Mg alloys were cast in air, hot extruded to thin plates, and oxidized in air at high temperatures. During the casting process, the CaO was decomposed into Ca in the α-Mg matrix and formed Al2Ca precipitates along grain boundaries. A thin, nonuniform CaO-rich layer was formed on the surface during the casting and oxidation. Based on this study, the oxidation mechanism of the CaO-added Mg alloys during casting and oxidation is proposed. (Received August 25, 2015)
Ti 주물표면의 반응성에 미치는 주형재료 및 점결제의 영향
김세광,김영직,김명균,김태경,홍태환 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.4
Attempts have been made to evaluate the relative stability of surface layer reactions of cast metal with mold material in commercially pure titanium and Ti-6Al-4V alloy castings. For melting of titanium alloys, plasma arc melting process was used and the extent of the surface reaction of castings was determined by optical metallography and microhardness profiles. The mold materials being examined included ZrO₂, Al₂O₃, CaO stabilized ZrO₂, CaZrO₃ and CaO. The machined graphite mold was used for comparison. Moreover, it was to investigate the effect of the binder on metal-mold reaction in case of Al₂O₃ mold. The results showed that titanium castings with ZrO₂, Al₂O₃ mold had clear reaction layer(α-case), whereas negligible reaction with titanium occurred in CaO stabilized ZrO₂, CaO, CaZrO₃ and graphite mold. The grading of thermal stability of mold material does not follow the free energy data of the formation of these oxide. CaZrO₃ is regarded as a promising mold material for titanium investment castings. In additions, metal-mold reaction of titanium castings was affected sufficiently by the binder as well as the mold material.
비정질/나도구조화된 Mg2NiHx 수소저장합금의 수소화 특성
김세광,김영직,홍태환,김명규 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.1
Amorphous or nanocrystalline solid states are gaining increased importance for hydrogen absorbing materials. Especially, in the case of Mg alloys, great improvements of hydrogenation properties can be achieved by nanocrystallization. In this study, Amor-/Nanocrystalline Mg₂NiH_X was fabricated from Mg and Ni chips by mechanical alloying for 96h under 2 MPa hydrogen atmosphere. The homogeneous Mg₂NiH_X was formed in 66 : 1 ball to chips weight ratio(BCR). The results of XRD and TEM revealed that the phases were composed of the amorphous and the nanocrystalline less than 10 ㎚. From the results of pressure-composition-isotherm(PCI) test, the hydrogenation properties were improved compared with the polycrystalline counterparts. But the hydrogen capacity was reduced from 3.6 mass% to 2.25 mass%(at 483K) in the BCR 66 : 1 specimen.
SiCp/AZ91D Mg 복합재료의 반용융 가압성형을 위한 조직제어
김세광,김영직,김명균,홍태환 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.11
The purpose of this study was to evaluate the microstructure evolution during partial remelting as a function of isothermal holding temperature and time in the semisolid state. SiC particle reinforced magnesium composites were manufactured by Rotation-Cylinder method(RCM) and fully solidified as the billet, and then the microstructure evolutions of them were evaluated through simple reheating procedure. The results showed that the presence of SiC particles led to the fine solid globules compared to those of unreinforced magnesium alloys, and the finer solid globules were achieved with increasing SiC particle fraction. Coalescence was reduced since the solid globules were more isolated with respect to each other by the presence of the particle in grainboundary regions, and Ostwald ripening was also altered by the reduction of the effective diffusion coefficient in the liquid. The average diameters of the solid globules were independent of holding temperature but the standard deviation of the average diameters and the number of the solid globules per area were reduced as temperature increased, mainly due to high liquid fraction. Based on the previous results, it might be suggested that thixoforming of the particle reinforced composites should be performed after short isothermal holding at a relatively high temperature.
Thixotropic AZ91HP Mg 합금의 수소화 특성
김세광,김영직,김명균,홍태환,하원 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.11
Thixotropic AZ91HP Mg alloy was only focused on aspect of semi liquid forming until now. In this study, for the purpose of proposition as economic lightweight hydrogen absorbing materials, the hydrogenation properties of thixotropic AZ91HP Mg alloy were evaluated by automatic Sieverts type pressure-composition-isotherm(PCI) apparatus. By the results of experiments, α-Mg rich phase(like solid phase) was regarded the storage system as an hydrogen absorbing / desorbing and eutectic phase (like liquid phase), Mg_(17)Al_(12)/Mg-Al-Zn, was considered to be the catalytic system as an improving factor of hydrogenation kinetics. Especially, the hydrogenation properties were dependent on the purity and size of α-Mg rich phase. In the case of 863, 868K specimens(4hr crushing under 2 ㎫ hydrogen atmosphere), liquid fraction was about 50-60% and the hydrogen capacity was reached about 4.5 wt% at 623K.