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마그네슘합금의 산화저항성에 미치는 산화칼슘 첨가의 영향
김기범 ( Kibeom Kim ),김상필 ( Sangpil Kim ),김권후 ( Kwonhoo Kim ) 한국열처리공학회 2020 熱處理工學會誌 Vol.33 No.3
Due to excellent properties such as high specific strength and low density, application of magnesium alloys have been rapidly increased. However, magnesium alloy has a serious problem that is easily oxidized when exposed to high-temperature. For this reason, magnesium alloys have been generally used for SF6 gas such as protective cover gas in casting and melting, but it has been reported that this gas has a serious influence on global warming. Therefore, many researchers have been studied to improve the oxidation resistance of magnesium alloy. It was reported that addition of Be, Ca and CaO in magnesium alloy can improve the oxidation properties. In this study, the possibility of improving the oxidation resistance by adding CaO extracted from oyster shells was investigated. Oyster shells were completely decomposed into CaO and CO<sub>2</sub> by annealing. With the addition of CaO, a coexistence region of MgO + CaO was formed in the oxide layer and its thickness was also reduced. (Received May 14, 2020; Revised May 20, 2020; Accepted May 25, 2020)
SWCNT 0.1%-PAN 3%-DMF 17% 교반용액을 활용한 전기방사 전압 및 강도특성연구
이종엽,배상대,김권후,Lee, Jongyeob,Bae, Sangdae,Kim, Kwonhoo 한국열처리공학회 2020 熱處理工學會誌 Vol.33 No.6
In this study, Electro spinning was carried out using Cabon nanotube 0.1%-Polyacrylonitrile 3%-Dimethylformamide 17% agitation solution. It was investigated the solute and solvent correlations according to the electro spinning voltages ranging form 5 to 40 kV, based on the SEM image. Except voltage 25 kV, electro spinning was failed due to the lack of electro spinning (less than 60%). Voltage 25 kV was showed excellent properties, and was confirmed Cabon nanotube 58.1 nm and diameter of Cabon nanotube + Polyacrylonitrile 1.76 ㎛ as shown SEM image. Also, the tensile test results were showed that SK Chemical prepreg electro spinning angle of 0 and 90 degrees were 137 MPa and 60 MPa, respectively.
AZ61 마그네슘 합금의 어닐링 중 Ca의 첨가에 따른미세조직 변화에 미치는 영향
김기범 ( Kibeom Kim ),전준호 ( Joonho Jeon ),김권후 ( Kwonhoo Kim ) 한국열처리공학회 2021 熱處理工學會誌 Vol.34 No.2
Due to high specific strength and low density, AZ series magnesium alloys have been receiving high interest as a lightweight material. However, their industrial application is limited due to the phenomenon that the strength decreases at elevated temperature by the occurrence of softening effect because of the Mg<sub>17</sub>Al<sub>12</sub> phase decomposition. To solve this problem, many research were conducted to increase the high-temperature strength by forming a thermal stable second-phase component by adding new elements to the AZ magnesium. Especially, adding Ca to AZ magnesium has been reported that Ca forms the new second-phase. However, studies about the analysis of decomposition or precipitation temperature, formation composition, and components to understand the formation behavior of these precipitated phases are still insufficient. Therefore, the effect of Ca addition to AZ61 on the phase change and microstructure of the alloy during annealing was investigated. As a result of analysis of the initial and heat-treated specimen, AZ61 formed α-Mg matrix and precipitated phase of Mg<sub>17</sub>Al<sub>12</sub>, and AZX611 formed one more type of precipitated phase, Al<sub>2</sub>Ca. Also, Al<sub>2</sub>Ca was thermal stable at high temperatures. And after annealing, the laves phase was decomposed to under 10 μm size and distributed in matrix. (Received February 3, 2021; Revised February 10, 2021; Accepted March 17, 2021)
변형속도에 따른 M1 마그네슘 합금의 고온변형 중 미세조직 형성 거동
이규정 ( Kyujung Lee ),김권후 ( Kwonhoo Kim ) 한국열처리공학회 2019 熱處理工學會誌 Vol.32 No.1
In this study, microstructure evolution and crystallographic orientation are investigated under various deformation conditions in M1 magnesium alloy. M1 magnesium ingot was rolled at 673 K with the rolling reduction of 30%. The compression test specimens were machined out from rolled plate, and then the specimens were annealed at 823 K for 1h. Uniaxial compression tests were conducted at 723 K and under the strain rate ranging from 5.0 × 10<sup>-4</sup> s<sup>-1</sup> to 5.0 × 10<sup>-2</sup> s<sup>-1</sup> up to a true strain of -1.0. For observation of crystal orientation distribution, EBSD measurement was performed. Occurrence of the dynamic recrystallization and grain boundary migration were confirmed in all case of the specimens. The distribution of the grains is not uniformed in the experimental conditions. (Received January 2, 2019; Revised January 15, 2019; Accepted January 22, 2019)
고온변형 중의 AZ80 마그네슘 합금의 미세조직 형성 거동에 미치는 변형속도의 영향
박민수 ( Minsoo Park ),김권후 ( Kwonhoo Kim ) 한국열처리공학회 2020 熱處理工學會誌 Vol.33 No.4
The crystallographic texture plays an important role in both the plastic deformation and the macroscopic anisotropy of magnesium alloys. In previous study for AZ80 magnesium alloy, it was found that the main texture components of the textures vary with the deformation conditions at high temperatures. Also, the basal texture was formed at stress of more than 15-20 MPa and the non-basal texture was formed at stress of less than 15-20 MPa. Therefore, in this study, uniaxial compression deformation of AZ80 magnesium alloy was carried out at high temperature (stress of 15-20 MPa). The uniaxial compression deformation is performed at temperature of 723 K and strain rate 3.0 × 10<sup>-3</sup>s<sup>-1</sup>, with a strain range of between -0.4 and -1.3. Texture measurement was carried out on the compression planes by the Schulz reflection method using nickel filtered Cu Kα radiation. EBSD measurement was also conducted in order to observe spatial distribution of orientation. As a result of high temperature deformation, the main component of texture and its development vary depending on deformation condition of this study. (Received June 17, 2020; Revised June 26, 2020; Accepted July 03, 2020)