• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1043-1044
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• 2006

Compositional dependence of corrosion behavior of rapidly solidified Mg-rich Mg-Zn-Y alloys in NaCl aqueous solution has been investigated. Mg-Zn-Y ternary alloys containing small amounts of Zn exhibited low corrosion rate, although the $Mg_{98}Y_2$ (at. %) binary alloy showed severe corrosion with violet evolution of hydrogen. The alloy with highest corrosion-resistance was $Mg_{97.25}Zn_{0.75_Y_2$, its corrosion rate was about 1 mm year-1 in 0.17 M (1.0 wt. %) NaCl solution. $Mg_{97.25}Zn_{0.75}Y_2$ alloy exhibited passive region in anodic polarization curves when immersed in NaCl solution. Rapidly solidification and small amount of Zn addition may bring about an increase in electrochemical homogeneity of Mg-Zn-Y alloys, resulting in enhancement of corrosion resistance.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.45-45
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• 2014

The importance of magnesium alloys has significantly increased due to their low density, high strength/weight ratio, very good electromagnetic shielding features and good recyclability. However, unfortunately, Mg alloys are very susceptible to corrosion due to their high chemically activities (= -2.356 V vs. NHE at $25^{\circ}C$), hence, most commercial Mg alloys require corrosion protective coatings. Organic coating such as painting, powder coating and electrophoretic deposition of paint (E-paint) is typically used in the final stages of the coating process of Mg alloys. In this study, effect of pre-immersion time on the deposition of E-paint on AZ31 Mg alloy was investigated. It was found that during pre-immersion time, AZ31 Mg alloy rapidly reacts with E-paint solution and paint can be self-deposited on the AZ31 surface without applying of electric current. The pore size on the E-painted AZ31 Mg alloy increased with increasing pre-immersion time from 0 to 5 min. Both adhesion and corrosion resistance of E-painted AZ31 Mg alloy decreased with increasing pre-immersion time. The best E-paint AZ31 Mg alloy, which showed stronger adhesion after water immersion test and good corrosion resistance, was started to deposit after 5 s of pre-immersion time.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.2
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• pp.51-57
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• 2021

The quality of the ceramic sintered coating on a metal surface through laser surface treatment is affected by the laser irradiation pattern. Depending on the laser irradiation pattern, the amount of residual stress and heat applied or accumulated on the surface increases or decreases, affecting the thickness attained in the ceramic sintering area. When the heat energy accumulated in the sintering area is high, the ceramic and the metal alloy melt and sufficiently mix to form a homogeneous and thick bonding interface. In this study, the thermal energy accumulation in the region sintered with zirconia was controlled using four types of laser processing patterns. The thickness of the diffusion region is analyzed by laser-induced breakdown spectroscopy of Mg-ZrO2 generated by laser sintering zirconia powder on the magnesium alloy surface. On the basis of the analysis of the Mg and Zr present in the sintered region through LIBS, the effect of the irradiation pattern on the sintering quality is confirmed by comparing and analyzing the heat and mass transfer tendency of the diffusion layer and the degree of diffusion according to the irradiation pattern. The derived diffusion coefficients differed by up to 9.8 times for each laser scanning pattern.

• Journal of Powder Materials
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• v.6 no.3
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• pp.231-237
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• 1999

In this study, the characteristics of gas atomized Mg-3wt%Al-1wt%Zn-1wt%MM alloy powders under vacuum condition were investigated. In spite of the low fluidity and easy oxidation of the molten magnesium, the spherical powders could be successfully produced by using a modified three pieces nozzle attached to the gas atomization unit. It was found that most of the solidified powders less than 50$\mu$m in diameter were single crystal and the solidified structure showed a typical dendritic morphology due to supercooling prior to nucleation. The secondary dendrite arm spacing decreased as the size of powders decreased. The Mg-Al-Ce intermetallic compounds with chemically stable phase were found in the interdendritic regions of $\alpha$-Mg. It is considered that formation of the chemically stable phase may possibly affect to improve the corrosion resistance. Therefore, it is expected that the materials formed of these Mg-Al-Zn-MM alloy powders shows better mechanical properties and corrosion resistance due to the structural refinement.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1045-1047
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• 2006

Fabrication of $Mg_{95.75}Zn_1Y_3Yb_{0.25}$ bulk alloy has been performed through the consolidation of rapidly solidified ribbons. The $Mg_{95.75}Zn_1Y_3Yb_{0.25}$ bulk alloy exhibited excellent mechanical properties, high tensile yield strength of 530 MPa, and large elongation of 3 %. Microstructure of the alloy was characterized by equiaxed fine grains that consist of -Mg, long period ordered (LPO) structure phase, and $Mg_5RE$-type cubic compound. The strengthening of the alloys may be due to fine grains with LPO structure phase and $Mg_5RE$-type compound.

• Journal of the Korean institute of surface engineering
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• v.50 no.1
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• pp.42-45
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• 2017

The magnesium-base AZ61 alloy was cast while adding 1% CaO powder into the melt. It was hot extruded, and oxidized at $550-650^{\circ}C$ in air in order to study its microstructure and oxidation behavior. Initially added CaO powder reacted with Al in the melt to $Al_2Ca$ particles that aligned along the extrusion direction. The formed $Al_2Ca$ particles increased the oxidation resistance through forming the superficial CaO scale at the upper part of the thin MgO oxide scale.

• Corrosion Science and Technology
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• v.17 no.3
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• pp.91-100
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• 2018

Development of biodegradable implants for treatment of complex bone fractures has recently become one of the priority areas in biomedical materials research. Multifunctional corrosion resistant and bioactive coatings containing hydroxyapatite $Ca_{10}(PO_4)_6(OH)_2$ and magnesium oxide MgO were obtained on Mg-Mn-Ce magnesium alloy by plasma electrolytic oxidation. The phase and elemental composition, morphology, and anticorrosion properties of the coatings were investigated by scanning electron microscopy, energy dispersive spectroscopy, potentiodynamic polarization, and electrochemical impedance spectroscopy. The PEO-layers were post-treated using superdispersed polytetrafluoroethylene powder. The duplex treatment considerably reduced the corrosion rate (>4 orders of magnitude) of the magnesium alloy. The use of composite coatings in inducing bioactivity and controlling the corrosion degradation of resorbable Mg implants are considered promising. We also applied the plasma electrolytic oxidation method for the formation of the composite bioinert coatings on the titanium nickelide surface in order to improve its electrochemical properties and to change the morphological structure. It was shown that formed coatings significantly reduced the quantity of nickel ions released into the organism.

• Journal of Powder Materials
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• v.14 no.6
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• pp.354-361
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• 2007

The bi-materials with Al-Mg alloy and its composites reinforced with SiC and $Al_2O_3$ particles were prepared by conventional powder metallurgy method. The A1-5 wt%Mg and composite mixtures were compacted under $150{\sim}450\;MPa$, and then the mixtures compacted under 400 MPa were sintered at $773{\sim}1173K$ for 5h. The obtained bi-materials with Al-Mg/SiCp composite showed the higher relative density than those with $Al-Mg/Al_2O_3$ composite after compaction and sintering. Based on the results, the bi-materials compacted under 400 MPa and sintered at 873K for 5h were used for mechanical tests. In the composite side of bi-materials, the SiC particles were densely distributed compared to the $Al_2O_3$ particles. The bi-materials with Al-Mg/SiC composite showed the higher micro-hardness than those with $Al-Mg/Al_2O_3$ composite. The mechanical properties were evaluated by the compressive test. The bi-materials revealed almost the same value of 0.2% proof stress with Al-Mg alloy. Their compressive strength was lower than that of Al-Mg alloy. Moreover, impact absorbed energy of bi-materials was smaller than that of composite. However, the bi-materials with Al-Mg/SiCp composite particularly showed almost similar impact absorbed energy to $Al-Mg/Al_2O_3$ composite. From the observation of microstructure, it was deduced that the bi-materials was preferentially fractured through micro-interface between matrix and composite in the vicinity of macro-interface.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1048-1049
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• 2006

Rapidly solidified ribbon-consolidation processing was applied for preparation of high strength bulk Mg-Zn-Gd alloys. Mg alloys have been used in automotive and aerospace industries. Rapid solidification (RS) process is suitable for the development of high strength Mg alloys, because the process realizes grain-refinement, increase in homogeneity, and so on. Recently, several nanocrystalline Mg-Zn-Y alloys with high specific tensile strength and large elongation have been developed by rapidly solidified powder metallurgy (RS P/M) process. Mg-Zn-Y RS P/M alloys are characterized by long period ordered (LPO) structure and sub-micron fine grains. The both additions of rare earth elements and zinc remarkably improved the mechanical properties of RS Mg alloys. Mg-Zn-Gd alloy also forms LPO structure in -Mg matrix coherently, therefore, it is expected that the RS Mg-Zn-Gd alloys have excellent mechanical properties. In this study, we have developed high strength RS Mg-Zn-Gd alloys with LPO structure and nanometer-scale precipitates by RS ribbon-consolidation processing. $Mg_{97}Zn_1Gd_2$ and $Mg_{95.5}Zn_{1.5}Gd_3$ and $Mg_{94}Zn_2Gd_4$ bulk alloys exhibited high tensile yield strength (470 MPa and 525 MPa and 566 MPa) and large elongation (5.5% and 2.8% and 2.4%).

• Journal of Korea Foundry Society
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• v.26 no.6
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• pp.267-271
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• 2006

Metal foam is a class of attractive materials, which exhibits unique combinations of physical, mechanical, thermal, electrical and acoustic properties. In particular, it is light and good at absorbing energy, which makes it attractive in automotive and aerospace applications weight is critical. In this paper, the Mg alloy foam was prepared by melt foaming method by addition of calcium as thickening agent, and $TiH_2$ or $CaCO_3$ powder as blowing agent. The macrostructural observation of foamed Mg showed that the pore structures of Mg alloy foam made by $CaCO_3$ as blowing agent were much better than that of foams made by $TiH_2$ as blowing agent. In addition, this paper showed the possible reason of fabrication magnesium alloy foam in proportion to blowing agent and the porosity range was about 40 to 76% as results value.