• Journal of the Korean Ceramic Society
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• v.17 no.1
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• pp.20-26
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• 1980

The crystallization behaviors of slag-based glass in $CaO-MgO-Al_2O_3-SiO_2(-Na_2O)$ system have been studied. The mother glass containing 16.50 CaO, 7.50MgO, 19.70Al2O3, 50.80SiO3 and 2.09wt% $Na_2O$ was prepared by using Korean domestic raw materials such as granulated slag, serpentine, sea sand and etc. The glass-ceramics composed of major crystalline phase diopside was produced by the heat treatment in a temperature range from 850$^{\circ}$ to 9$25^{\circ}C$ for 0-6hr. The composition and morphology of diopside phase formed in the system were examined by X-ray diffraction analysis and electron microscopy. The kinetic measurements such as J.M. A plot and Arrhenius plot indicated that the process of nucleation of the initially formed diopside phase could be described from the view point of instantaneous nucleation. It was also demonstrated that the linear crystal growth of diopside phase was proceeded by short range diffusion of $Mg^{2+}$ and $Ca^{2+}$ ion. The microstructures of the resulting glass-ceramics were consisted of leafroidal shaped crystalline aggregations.

• Journal of the Korean Society for Heat Treatment
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• v.34 no.2
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• pp.53-59
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• 2021

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 Mg17Al12 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 Mg17Al12, and AZX611 formed one more type of precipitated phase, Al2Ca. Also, Al2Ca was thermal stable at high temperatures. And after annealing, the laves phase was decomposed to under 10 ㎛ size and distributed in matrix.

• Journal of Korea Foundry Society
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• v.34 no.6
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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.

• Journal of Korea Foundry Society
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• v.27 no.5
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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.

• Journal of the Korean Society for Heat Treatment
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• v.27 no.4
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• pp.185-190
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• 2014

The influences of small amount of Sn addition on microstructure and creep resistance of AZ91-0.4%Ca alloy have been investigated. The microstructure of the AZ91-0.4%Ca alloy was characterized by ${\alpha}$-(Mg) dendrite cells surrounded by eutectic ${\beta}(Mg_{17}Al_{12})$ and $Al_2Ca$ phases. The 0.5%Sn addition resulted in the formation of rod-shaped CaMgSn particles with the extinction of $Al_2Ca$. The Sn-containing alloy exhibited better creep resistance below $175^{\circ}C$, but the tendency was reversed above $200^{\circ}C$. The reason was discussed in relation to the change in thermal stability of ${\beta}$ phase in response to the Sn addition.

• Journal of Korea Foundry Society
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• v.23 no.5
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• pp.251-256
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• 2003

Effects of Ca addition on grain refinement, microstructure and mechanical properties of AZ31 Mg alloy were investigated. Due to Ca addition to Mg alloy (AZ31), the microstructure was refined, the quantity of $Mg_{17}Al_{12}$phase was reduced, and new $Al_2Ca$ phase was formed. The tensile property of AZ31 was increased with the minor addition of Ca, but was decreased rapidly over 0.2 wt.% of Ca content. The $Al_2Ca$ phase was considered to be detrimental to the mechanical property of AZ31 Mg alloy.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.3
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• pp.127-131
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• 2001

The effect of grain shape on the grain growth behavior of oxide system was investigated as afunction of liquid content during liquid phase sintering. As a model system, the solid grains of $Al_{2}O_{3}$ and MgO were selected during liquid phase sintering, i.e. faceted shape of $Al_{2}O_{3}$ in $CaAl_{2}Si_{2}O_{8}$ liquid phase and spherical shape of MgO in $CaMgSiO_{4}$ liquid phase. The average grain size of MgO with spherical shape was decreased with increasing the liquid phase content, whereas that of $Al_{2}O_{3}$ with faceted shape was independent of liquid phase content. In the case of $Al_{2}O_{3}$ grains with faceted shape, which interfaces are expected to be atomically flat, are likely to grow by the interfacial reaction controled process. Whereas, in the case of MgO grains with spherical shape, which interface are expected to be atomically rough, are likely to grow by the diffusion controlled process.

• Journal of the Korean Ceramic Society
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• v.34 no.2
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• pp.145-156
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• 1997

ZrO2 phase transformations depending on the type and amount of dopants and the sintering temperatures were studied for the 2 components (CaO-, Y2O3-, MgO-ZrO2) and the 3 components(MgO-ZrO2-Al2O3)ZrO2 powder by X-ray diffraction and Raman spectroscopy. In the CaO- and Y2O3-ZrO2 systems, as the CaO and Y2O3 contents increased to 6~15mol% and 3~15mol% respectively, we were not able to identify between tetragonal and cubic in the X-ray diffraction patterns. On the other hand, all Raman modes shifted to lower wavenumbers, decreasing in intensity and the number of bands, markedly. These phenomena were caused by tetragonallongrightarrowcubic phase transformation and interpreted by the breakdown of the wave vector selection rule(k=0) and the structural disorder associated with the formation of oxygen sublattice which was caused by the substitution between Zr4+ ion and Ca2+ or Y3+ ion in ZrO2 matrix. The monoclinic to cubic phase transformation occurred in 10mol% MgO-ZrO2 system. As the Al2O3 content increased from 0 to 20mol% in the MgO-ZrO2-Al2O3 systems, cubic phase transformed to monoclinic phase, this is because the MgO didn't play a role in a stabilizer because of the formation of the spinel(MgAl2O4) by the reaction between MgO and Al2O3, Also, the ZrO2 phase transformation was explained by the change of it's lattice parameters depending on the type and amount of dopants. Namely, as the amount of dopant increased to 10~13mol%, the axial ra-tio c/a came close to unity with increasing the lattice parameter a and decreasing the lattice parameter c. At that time, the tetragonallongrightarrowcubic phase transformation occurred.

• Journal of the Korean Ceramic Society
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• v.36 no.4
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• pp.410-416
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• 1999

The reactivity of three kinds of spinels which CaO-Al2O3-SiO2 slag was investigated in terms of mineral phases and microstructures. New crystal products were not formed by reaction of 12CaO.7Al2O3 in the slag with spinels and free MgO components was preferenctially dissolved into slag for MgO-rich spinel and stoichiometric spinel. Meanwhile mineral phase was changed from 12CaO.7Al2O3 to CaO.Al2O3 to CaO.2Al2O3 finally to CaO.6Al2O3 having high melting point for Al2O3 -rich spinel. The Fe-oxide component of the slag was taken up by only stoichiometric spinel grains within the spinel clinker and the trapped amount of Fe-oxide was independent of MgO content of MgO in spinel clinker the more th resistance to slag corrosion but the less resistance to slag penetration.

• Korean Journal of Metals and Materials
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• v.47 no.2
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• pp.114-120
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• 2009

The viscosities of $CaO-SiO_2-Al_2O_3-MgO$ flux were measured under the condition of $CaO/SiO_2=1.0-1.3$ and 5-20 wt%MgO. Submerged arc welding flux with $5wt%Al_2O_3$ content had the lowest critical temperature and widest solid-liquid coexisting region at about 5 wt%MgO. It indicateds that both critical temperature and viscosity depend on the kind of primary phase of molten flux. Viscous behavior of the molten flux at 1773 K was analyzed in the view of silicate structure changed by FT-IR spectroscopy. Based on the critical temperature and the behavior of viscosity at a fixed temperature, it could be proposed that the contents of MgO and $Al_2O_3$ in SAW flux show a pronounced effect on preventing contamination in maintaining the liquid phase flux after welding process.