• Journal of Power System Engineering
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• v.10 no.3
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• pp.45-50
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• 2006

In this paper, creep tests of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloy casted by mold under the temperature range of 473.00-573.00K, and the stress range of 23.42-87.00Mpa were done with the equipment of automatic controlled temperature and computer for data acquisition. The activation energies were obtained by relationship between creep rate and temperature, and the stress exponents were obtained by relationship between creep rate and stress. From the experiment results, the activation energies of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloy were 149.87kJ/mol, 147.97kJ/mol, respectively, and the stress exponents of those alloy were 5.13, 5.59, respectively, under the temperature of 473.00-493.00K and the stress range of 62.43-78.00Mpa. And the activation energies of those alloy were 134.41kJ/mol, 129.22kJ/mol, respectively, and the stress exponent of those alloy were 3.48, 3.77, respectively, under the temperature of 553-573Mpa and the stress range of 23.42-39.00Mpa. Also the lifes of Mg-Zn-Mn-Ca alloy were higher than those of Mg-Zn-Mn alloy, and the results of SEM showed fracture surfaces under low temperature had smaller dimples than those under high temperature.

• Journal of Welding and Joining
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• v.31 no.6
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• pp.27-31
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• 2013

Magnesium alloy is used on parts of aircraft and electronic equipment because of the highest specific strength among the common metal materials. Recently, studies about appling magnesium alloy sheet to automotive bodies are on the increase rapidly. For application to automotive bodies, researches about characteristics of resistance spot welding of magnesium alloy sheet are essential. Magnesium alloy has low boiling point, so getting sound bead shape is difficult when appling varies welding processes. Resistance spot welding is also particular about setting optimum welding conditions because of spatter generation, pores and cracks occurrence in nugget. And life of electrodes is very short because of alloying with copper that main material of electrodes. This requires frequent dressing and replacement of electrodes and decrease in productivity of resistance spot welding on magnesium alloy. Therefore in this study, for effective analysis of changes in tensile shear load and nugget size during electrode life test, evaluate detail characteristics of resistance spot welding on magnesium alloy sheet using dome type electrode.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.6
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• pp.636-641
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• 2016

Alkaline water electrolysis is commercial hydrogen production technology. It is possible to operate MW scale plant. Because It used non-precious metal for electrode. But It has relatively low current density and low efficiency. In this study, research objective is development of anode for alkaline water electrolysis with low cost, high corrosion resistance and high efficiency. Stainless steel 316L (SUS 316L) was selected for a substrate of electrode. To improve corrosion resistance of substrate, Nickel (Ni) layer was electrodeposited on SUS 316L. Ni-Fe alloy was electrodeposited on the passivated Ni layer as active catalyst for oxygen evolution reaction(OER). We optimized preparation condition of Ni-Fe alloy electrodeposition by changing current density, electrodeposition time and composition ratio of Ni-Fe electrodeposition bath. This electrodes were electrochemically evaluated by using Linear sweep voltammetry (LSV) and Cyclic voltammetry (CV). The Ni-Fe alloy (Ni : Fe = 1 : 1) showed best activity of OER. The optimized electrode decreased overpotential about 40% at $100mA/cm^2$ compared with Ni anode.

• Journal of Powder Materials
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• v.30 no.2
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• pp.140-145
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• 2023

Although the Ti-6Al-4V alloy has been used in the aircraft industry owing to its excellent mechanical properties and low density, the low formability of the alloy hinders broadening its applications. Recently, laser-powder bed fusion (L-PBF) has become a novel process for overcoming the limitations of the alloy (i.e., low formability), owing to the high degree of design freedom for the geometry of products having outstanding performance used in high-tech applications. In this study, to investigate the effect of bulk shape on the microstructure and mechanical properties of L-PBFed Ti-6Al-4V alloys, two types of samples are fabricated using L-PBF: thick and thin samples. The thick sample exhibits lower strength and higher ductility than the thin sample owing to the larger grain size and lower residual dislocation density of the thick sample because of the heat input during the L-PBF process.

• Journal of Welding and Joining
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• v.33 no.1
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• pp.14-23
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• 2015

Recent developing tendency of nuclear power plant are studied by searching of NDSL, KIPRIS, Science Direct and so on. Welding materials such as low alloyed steels, stainless steels, nickel-based alloys, zirconium alloy and welding methods such as narrow gap welding, laser beam welding, friction stir welding, overlay welding are investigated.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.231-232
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• 2006

Aluminum Alloys with a content of 22 wt.-% $Mg_2Si$ were spray formed. This alloy features by a low density and is therefore a superior material for leightweight applications. The main problem in spray forming of this type of alloy was the occurance of high porosities. First process optimizations have been performed to decrease porosity under a certain level, so that it can be closed by an extrusion process

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.124.2-124.2
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• 2016

Corrosion resistance and adhesion of electro-paint (E-paint) with fluoride conversion coating (FCC) on AZ31 Mg alloy were studied. Corrosion resistance and adhesion were studied as a function of FCC-treatment time and concentration of FCC-bath. Aqueous hydrogen fluoride (HF) solutions, with concentrations ranging from 0.5 M to 5 M, were used to form FCC on chemically polished AZ31 Mg alloy samples for six different times; 10, 30, 60, 90, 120, and 180s. The results from salt spray test (SST) showed that corrosion resistance of E-paint appeared to decrease with increasing FCC treatment times in low concentration FCC baths. The number of blisters formed on the FCC-treated samples increased with increasing FCC treatment time of more than 1 min in low concentration (0.5 M to 1 M) solutions. On the other hand, samples treated in the 5 M HF solution for 120s showed no delamination or blistering even after 1200h of SST.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1082-1086
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• 2004

Since the sheet forming of Mg alloy has many difficulties due to the low formability, many forming conditions need to be selected properly. Especially, the process variables should be investigated to increase the formability, such as, forming temperature. In this paper, the effects of forming process variables has been investigated using the bending and deep drawing process. A simple U-bending designed for mobile part could be formed in room temperature and springback amounts are surveyed. On the other hand, square cup part couldn't be formed in room temperature due to the low formability. Therefore, the effects of forming temperature are investigated in deep drawing process for square cup part. As a experimental and FEM results, the optimum forming temperature is presence and formability in a higher temperature is less than that of lower temperature. Above experimental results are compared with the FEM analysis and well coincided with the experimental results. Therefore, more detail investigations could be progressed to select more appropriate process conditions by the FEA.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.220-225
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• 2007

The mechanical characteristics of AC4C Aluminum Casting Alloy were investigated by tensile test and impact test. Based on the tensile test' s result, we found that the yield strength of a high speed was about 10% higher than that of a low speed test and the maximum rupture strain mostly occurred in low speed tensile test. The impact energy of curved surface specimen was higher than that of plane surface specimen that can be measured in impact test.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.13-19
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• 2007

To find out the optimum design of hydrogen storage and supply tank using Metal Hydride (briefly MH) and to make clear the performance characteristics under various conditions are our research purpose. In order to use the low-temperature exhaust heat, $LaNi_{4.7}Al_{0.3}$ which operates under the low pressure of 1 MPa is chosen, and we measure the basic properties, namely density, specific heat, PCT(Pressure-Concentration-Temperature) characteristics, and effective thermal conductivity. Then, a numerical calculation model of hydrogen storage using MH alloy is suggested and this thermal diffusion equation of model is solved by the backward difference method. This calculation results are compared with the experimental results of the systems which installed 1kg MH alloy and, it is found out that our calculation model can well predict the experimental results. By the experimental using MH alloy, it is recognized that the hydrogen flow rate can control by the step adjustment of brine temperature.