• 한국주조공학회지
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• 제32권1호
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• pp.44-49
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• 2012

In this study, three magnesium alloys were investigated; those are 1.5wt.% CaO added AM80, 1.0wt.% CaO added AM60, and conventional MRI153 alloys. Test specimens of three alloys were prepared by re-melting and casting into steel mold with ingots and machining. The mechanical properties and the creep behavior at 150 degrees Celsius of these specimens were determined and their microstructures were characterized using OM and SEM. For the application to die-casting, fluidity test were carried out with spiral mold. Compared with 1.0wt.% CaO added AM60 alloy, 1.5wt.% CaO added AM80 alloy exhibited good creep properties in all test conditions. Moreover, CaO added alloys showed better creep properties than MRI153 alloy at lower load condition. It is proposed that 1.5wt.% CaO added AM80 alloy is useful to apply to power-train parts such as transmission case in vehicles.

• 한국주조공학회지
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• 제27권5호
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• pp.198-202
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• 2007

In the present study, the high temperature mechanical properties and creep resistance of Mg-Zn-Y-Ca alloys has been investigated. The Mg-4Zn-0.8Y alloy consists of ${\alpha}$-Mg matrix and icosahedral quasicrystalline phase. Calcium addition into Mg-4n-0.8Y based alloy results in the formation of ${\tau}(Ca_{2}Mg_{6}Zn_{3})$ and $Mg_{2}Ca$ as the second solidification phases. Creep properties of the Mg-Zn-Y and Mg-Zn-Ca based alloys measured at applied stresses between 65 MPa and 85 MPa are significantly improved with adding calcium and yttrium, respectively. The improved creep resistance is due to the formation of thermally stable $Mg_{2}Ca$ phase.

• 열처리공학회지
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• 제17권5호
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• pp.299-304
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• 2004

Influence of Ca addition on microstructure and room temperature mechanical properties has been studied for AZ31(Mg-3%Al-1%Zn-0.2%Mn)-(0~0.5)%Ca wrought alloys, based on experimental results from metallography, X-ray diffractometry and mechanical tests. Yield strength, ultimate tensile strength and hardness of the alloys increased remarkably with increasing Ca content, whereas elongation was deteriorated continuously. Microstructural examination revealed that Ca addition efficiently refined grains of ${\alpha}$(Mg) phase and that some of the Ca dissolved in ${\beta}(Mg_{17}Al_{12})$ precipitates. The former and the latter facts are thought to be responsible for improved strength and loss of ductility of the AZ31+Ca wrought alloys, respectively.

• Corrosion Science and Technology
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• 제7권3호
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• pp.152-157
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• 2008

New wrought magnesium alloys have increasingly been developed in recent years for the automotive industry due to their high potential as structural materials for low density and high strength/weight ratio demands. However, their poor mechanical properties and low corrosion resistance have led to a search for new kinds of magnesium alloys with better strength, ductility, and high corrosion resistance. The main objective of this research is to investigate the corrosion behaviour of new magnesium alloys: Mg-Zn-Ag (ZQ), Mg-Zn-Mn-Si (ZSM) and Mg-Zn-Mn-Si-Ca (ZSMX). These ZQ6X, ZSM6X1, and ZSM651+YCa alloys were prepared using hot extrusion. AC, DC polarization and immersion tests were carried out on the extruded rods. Microstructure was examined using optical and electron microscopy (SEM) and EDS. The addition of silver decreased the corrosion resistance. The additions of silicon and calcium also affected the corrosion behaviour. These results can be explained by the effects of alloying elements on the microstructure of Mg-Zn alloys such as grain size and precipitates caused by the change in precipitation and recrystallisation behaviour.

• 한국주조공학회지
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• 제27권3호
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• pp.131-134
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• 2007

[ $SF_6$ ] gas that is used as a protective cover gas for Mg and Mg alloys during melting and casting has extremely high greenhouse effect. CaO added Mg alloys could maintain their original mechanical properties and original abilities such as fluidity and hot tearing susceptibility. The ignition temperature increased with increasing CaO addition under ambient atmosphere and nitrogen atmosphere. The minimum amount of $SF_6$ gas decreased by 0.13 wt%CaO added AZ91D Mg alloy in the sealed condition.

• 한국주조공학회지
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• 제34권6호
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• pp.187-193
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• 2014

In the present work, the effect of adding Ce on the corrosion behavior of Mg-4Al-2Sn-1Ca alloy was investigated. The studied alloys were fabricated by gravity casting method and a potentiodynamic polarization, A.C. impedance and hydrogen evolution tests were carried out in a 3.5% NaCl solution with pH 7.2 at room temperature to measure the corrosion properties of Mg-4Al-2Sn-1Ca-xCe alloys. The microstructure of the Mg-4Al-2Sn-1Ca alloy was composed of ${\alpha}$-Mg, Mg17Al12, Mg2Sn and CaMgSn phase. Also, a $Al_{11}Ce_3$ phase was newly formed by the addition of Ce. With an increase of the Ce contents, the microstructure became refined and the corrosion resistance improved.

• 한국주조공학회지
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• 제18권4호
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• pp.364-372
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• 1998

Effects of Si and Ca additions on the mechanical properties of AM60 based Mg alloys have been investigated. Hardness of the AM60 based Mg alloys reached a maximum value after aging for approximately 33 hours but the amount of hardness increase was negligible. The poor age hardening response of the alloys was due to low Al content, which implies that Al content must be >6 wt.% to observe age hardening effect. The tensile and yield strength increased with increasing Al, Si, and Ca content but elongation decreased with increasing Al and Si content. The best mechanical properties obtained in AM 40-2.5Si-0.2Ca alloy after T4 heat treatment were as follows; tensile strength 193.4 MPa, yield strength 79.2 MPa, and elongation 11.2%. High temperature property obtained from creep test was also improved by introducing $Mg_2Si$ which has high hardness, high melting temperature and low thermal expansion coefficient.

• 한국재료학회지
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• 제25권6호
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• pp.269-273
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• 2015

The effect of adding Ca on the microstructural and mechanical properties of as-cast Mg-11Li-3Zn-1Sn(wt%) alloys were investigated. Mg-11Li-3Zn-1Sn-0.4Mn with different Ca additions (0.4, 0.8, 1.2 wt%) were cast under an $SF_6$ and $Co_2$ atmosphere at $720^{\circ}C$. The cast billets were homogenized at $400^{\circ}C$ for 12h and extruded at $200^{\circ}C$. The microstructural and mechanical properties were analyzed by OM, XRD, SEM, and tensile tests. The addition of Ca to the Mg-11Li-3Zn-1Sn-0.4Mn alloy resulted in the formation of $Ca_2Mg_6Zn_3$, MgSnCa intermetallic compound. By increasing Ca addition, the volume fraction and size of $Ca_2Mg_6Zn_3$ with needle shape were increased. This $Ca_2Mg_6Zn_3$ intermetallic compound was elongated to the extrusion direction and refined to fine particles due to severe deformation during hot extrusion. The elongation of the 0.8 wt% Ca containing alloy improved remarkably without reduction strength due to the formation of fine grain and $Ca_2Mg_6Zn_3$ intermetallic compounds by Ca addition. It is probable that fine and homogeneous $Ca_2Mg_6Zn_3$ intermetallic compounds played a significant role in the increase of mechanical properties.

• 전기화학회지
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• 제2권2호
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• pp.106-111
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• 1999

[ $CaNi_5$ ] 수소저장합금의 전기화학적 충$\cdot$방전 특성에 미치는 MG(mechanical grinding) 영향이 Ar및 $H_2$ 가스분위기에서 조사되었다 MG공정중 $CaNi_5$ 합금은 표면 산화층의 파괴와 재생성 및 산화층 근방의 불균질화로 인하여 MG 15시간 이후부터 CaO와 Ni로 뚜렷한 상분리가 일어났다. $MG-CaNi_5$는 MG시간이 길어질수록 초기의 전기화학적 방전용량은 현저히 감소하였지만 충$\cdot$방전 싸이클의 증가에 따른 용량저하 속도는 $CaNi_5$합금에 비하여 낮았다. MG처리된 $CaNi_5$합금의 퇴화는 MG공정중의 상분리 및 불규칙화에 의한 수소의 가역반응 site의 감소 및 분극저항의 증가, KOH 전해질 내에서 합금 표면의 산화반응에 의한 부동태 피막형성에 기인하는 것으로 판단되었다.

• 대한금속재료학회지
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• 제56권11호
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• pp.829-834
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• 2018

Although magnesium-based alloys are attractive materials for hydrogen storage applications, their activation properties, hydrogenation/dehydrogenation kinetics, thermodynamic equilibrium parameters, and degradation characteristics must be improved for practical applications. Further, magnesium poses several risks, including explosion hazard, environmental pollution, insufficient formability, and industrial damage. To overcome these problems, CaO-added Mg alloys, also called Eco-Mg (environment-conscious Mg) alloys, have been developed. In this study, $Eco-MgH_x$ composites were fabricated from Mg-CaO chips by hydrogen-induced mechanical alloying in a high-pressure atmosphere. The balls-to-chips mass ratio (BCR) was varied between a low and high value. The particles obtained were characterized by X-ray diffraction (XRD), and the absorbed hydrogen was quantified by thermogravimetric analysis. The XRD results revealed that the $MgH_2$ peaks broadened for the high BCR. Further, PSA results revealed particles size were decreased from $52{\mu}m$ to $15{\mu}m$.