• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.6
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• pp.324-327
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• 2009

In the present study, the effect of Ca additions on the ignition and combustion behaviors of Mg alloys has been investigated. Cracks and inclusions were observed at the free surface and interior in as-cast pure magnesium but not in Ca-bearing Mg alloys. There was a tendency that ignition temperature rapidly increased with increasing Ca content in Mg-Ca alloy. Saturated composition for increasing of ignition temperature was related with solid solubility of Ca in Ca-bearing Mg alloys. The protective oxide layers, MgO, could also be found on the combustion surface of Ca-bearing magnesium alloy.

• Corrosion Science and Technology
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• v.17 no.4
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• pp.154-165
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• 2018

During the process of sulfur dioxide removal, flue gas desulfurization equipment provides a serious internal corrosion environment in creating sulfuric acid dew point corrosion. Therefore, the utilities must use the excellent corrosion resistance of steel desulfurization facilities in the atmosphere. Until now, the trend in developing anti-sulfuric acid steels was essentially the addition of Cu, in order to improve the corrosion resistance. The experimental alloy used in this study is Fe-0.03C-1.0Mn-0.3Si-0.15Ni-0.31Cu alloys to which Ru, Zn and Ta were added. In order to investigate the effect of $H_2SO_4$ concentration and the alloying elements, chemical and electrochemical corrosion tests were performed. In a low concentration of $H_2SO_4$ solution, the major factor affecting the corrosion rate of low alloy steels was the exchange current density for $H^+/H_2$ reaction, while in a high concentration of $H_2SO_4$ solution, the major factors were the thin and dense passive film and resulting passivation behavior. The alloying elements reducing the exchange current density in low concentration of $H_2SO_4$, and the alloying elements decreasing the passive current density in high concentration of $H_2SO_4$, together play an important role in determining the corrosion rate of Cu-bearing low alloy steels in a wide range of $H_2SO_4$ solution.

• Proceedings of the KSR Conference
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• 1999.11a
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• pp.181-188
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• 1999

For weight reduction of the gearbox of power bogie of high speed train, aluminum alloy is recommended for the material of the gerabox case. In this paper, three models(Steel G/B Case-Steel BRG. Case[model-S], Aluminum G/B Case-Aluminum BRG. Case[model-A], Aluminum G/B Case-Steel BRG. Case[model-AS]) were compared to each other in the view of thermal expansion. The evaluation of the internal load, thermal expansion deformation and lug analysis were executed. It results that the 'model-A' is excessively deformed and fail in the bolt hole of bearing case. Material change of the bearing case to steel(model-AS) is effective to restrain the deformation of the inner radios of the bearing case and to prevent the failure of that.

• Nuclear Engineering and Technology
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• v.51 no.5
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• pp.1345-1354
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• 2019

Clogging of sump strainers that filter the recirculation water in containment after a loss-of-coolant accident (LOCA) seriously impedes the continued cooling of nuclear reactor cores. In experiments examining the corrosion of aluminium alloy 6061, a common material in containment equipment, in borated solutions simulating the water chemistry of sump water after a LOCA, we found that Fe-bearing intermetallic particles, which were initially buried in the Al matrix, were progressively exposed as corrosion continued. Their cathodic nature $vis-{\grave{a}}-vis$ the Al matrix provoked continuous trenching around them until they were finally released into the test solution. Such particles released from Al alloy components in a reactor containment after a LOCA will be transported to the sump entrance with the recirculation flow and trapped by the debris bed that typically forms on the strainer surface, potentially aggravating strainer clogging. These Fe-bearing intermetallic particles, many of which had a rod or thin strip-like geometry, were identified to be mainly the cubic phase ${\alpha}_c-Al(Fe,Mn)Si$ with an average size of about $2.15{\mu}m$; 11.5 g of particles with a volume of about $3.2cm^3$ would be released with the dissolution of every 1 kg 6061 aluminium alloy.

• Journal of the Korean institute of surface engineering
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• v.12 no.3
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• pp.161-166
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• 1979

Theoretical and practical aspects are investigated for electrochemical behavious, plating processes and the structures of electrodeposit of Pb-Sn binary alloy plating through numerous literatures in this report. The anodic and cathodic electrode reaction mechanisms of Pb and Sn could co-deposit and make Pb-Sn alloy deposit from the results of cathode current density-cathode potential curves of Pb, Sn and Pb-Sn alloys in fluoborate solutions. The compositions of the best alloy plating solutions are obtained for the purpose of bearing, anticorrosion and solder plating. In general, the casting anodes of Pb-Sn alloys are used, but separated anodes of Pb and Sn pure metal are used in order to obtain the fine compositions of Pb-Sn alloy deposits. The electrodeposits of Pb-Sn alloy are in nonequilibrium state and saturated solid solutions. Thus, ${\beta}$-phase (Sn-phase) is precipitated by heat treatment. The texture and structure of the electrodeposit are associated with the surface energies of deposit lattice planes and with the cathode polarization. The electrodeposit of Pb-Sn alloy is shown as lamellar structure.

• Journal of the Korean Society for Heat Treatment
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• v.33 no.3
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• pp.117-123
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• 2020

Due to high corrosion resistance, Zinc has been widely used in the automobile, shipping or construction industries as a galvanizing material. Zinc is popular as a coating element, but its low mechanical strength impede the expansion of applications as a load-bearing structure. The mechanical strength of Zinc can be increased through zinc based alloy process, but the ductility is significantly reduced. In this study, the mechanical strength and ductility of Zinc-Magnesium alloys with respect to heat treatment hold time was investigated. In order to enhance the mechanical strength of Zinc, a Zinc-Magnesium alloy was fabricated by a melting process. The heat treatment process was performed to improve the ductility of Zinc-Magnesium alloy. The microstructure of the heat-treated alloy specimen was analyzed using SEM. The hardness and compressive strength of the specimen were measured by a micro-hardness tester and a nano-indenter, respectively.

• Journal of Korea Foundry Society
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• v.22 no.4
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• pp.174-183
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• 2002

Twin-roll process is a relatively new continuous casting process which can produce high-quality strip products directly, and solidification rate can reach $10^3$ to $10^4$ K/s, leading to fine and uniform microstructures with enhanced mechanical properties. The strip casting condition for producing fine Al-Sn alloy strip was obtained experimentally, and defects appearing on the strip was examined. Crack formation and surface quality of the strip was found to depend mainly on process parameters such as melt temperature, roller gap and rolling speed. Sn structure of network type was observed in Al-20Sn and Al-40Sn alloy strips, and cell spacing of Al-40Sn alloy was smaller than that of Al-20Sn. Banding strength of the heat treated specimens increased with increasing of soaking time and temperature, and bonding strength of Al-20Sn alloy was more superior than that of Al-40Sn alloy. However wear resistance of Al-40Sn alloy contained large amount of soft Sn which possess good anti-friction characteristics was superior than that of Al-20Sn alloy.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.7
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• pp.94-100
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• 1999

This study adopted the ultra precision machining system which was composed of an air bearing spindle, a granite bed, air pad and a linear feeding mechanism. It also applied the cutting experiment on the aluminum alloy. To evaluate the safety of high speed machining, we examined the surface roughness according to the changes of cutting speed and obtained the speed limit. This paper also studied the effect of cutting condition such as feed rates and depths of cut on the surface roughness within the speed limit. This provided practical information regarding ultra precision machining.

• Tribology and Lubricants
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• v.9 no.1
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• pp.55-61
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• 1993

Recently, due to the erosion damage that were generated increasingly at alloy metals of slide bearing by cavity of lubricating oil with tendency of high speed and high output of reciprocating engine, there is a need to study the process on the formation of cavitation erosion, and the characteristic of cavitation erosion at lubricating oil environments under various condition for marine ship. Therefore, the apparatus of cavitation erosion experiment used 20 KHz, $24 \mu m$ piezoelectric vibrator. The main results obtained through this test method are as follows: 1. The max. erosion rate at lubricating oil environments was related to the change of space, oil film thickness, and shown to tendency of gear oil>system oil>turbine oil>mixed oil environments with different viscosity. 2. The pitted hole by cavitation erosion at high viscosity oil environments became small and deep, and in addition to, they appeared to be wide and shallow at low viscosity.

• Tribology and Lubricants
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• v.11 no.1
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• pp.58-65
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• 1995

When marine lubricating oil began to be emulsified and oxidized through ingressive water that have leaked from cooling pump seal systems, cooler, purifier system and piping system, the cavitation erosion-corrosion in alloy metals of bearings remains to the various troublesome problem at effective engine performance. Therefore, applied the cathodic protection to the control test of cavitation erosion-corrosion, and appointed the marine system oil containing 3% sea water as test environments, with different conductibility. Also, used the piezoelectric vibrator with 20 KHz, 24 $\mu$m as the cavity generation apparatus, and examined the weight loss, potential value, current density etc. in specimens with those condition. According to this testing data, investigated influence of cathodic protection on the control characteristics of cavitation erosion-corrosion, and will serve those as an elementary design data of marine bearing.