• Journal of the Korean Society of Safety
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• v.24 no.6
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• pp.20-26
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• 2009

The creep deformation behavior of AZ31 magnesium alloy was examined in the temperature range from 573 to 673K (0.62 to 0.73 Tm) under various constant stresses covering low strain rate range from $4{\times}10^{-9}\;s^{-1}$ to $2{\times}10^{-2}\;s^{-1}$. At low stress level, the stress exponent for the steady-state creep rate was ~3 and the present results were in good agreement with the prediction of Takeuchi and Argon model. At high stress level, the stress exponent was ~5 and the present results were in good agreement with the prediction of Weertman model. The transition of deformation mechanism from solute drag creep to dislocation climb creep could be explained in terms of solute-atmospherebreakaway concept.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2009.10a
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• pp.105-106
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• 2009

AZ31 (3% Al, 1% Zn) Mg 판재의 내식성 향상을 위해 Ti/Zr/Polymer 복합계의 Cr-free 화성처리 방법을 이용하였다. 염수분무시험을 통해 최고 72시간 ($5{\sim}10%$ 발청) 내식성이 나타남을 확인하였다. 화성피막의 내식성은 그 피막이 가진 성분, 균일도, 치밀도, 형상 및 두께에 의해 좌우되는 만큼 TEM, SEM을 통해 화성피막 구조가 내식성과 어떠한 관련이 있는지 조사하였다. 또한, 화성처리 전 단계 공정인 탈지와 산세 및 중화 공정의 변수 조절을 통해 전처리 공정이 최종 화성피막의 물성에 어떠한 영향을 미치는지 조사하였다. 탈지조건을 $35{\sim}40^{\circ}C$, 5분에서 $50{\sim}80^{\circ}C$, $10{\sim}20$분으로 변경 시 좀 더 균일한 외관을 얻을 수 있었고, 적절한 중화제 선택을 통해 화성피막을 균일하게 형성시킬 수 있었다. 투과전자현미경 결과로 미루어 화성피막의 두께보다 균일도와 치밀도가 내식성에 결정적인 영향을 미치는 것을 확인할 수 있었다.

• Korean Journal of Metals and Materials
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• v.48 no.4
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• pp.305-314
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• 2010

The development of textures and microstructures during plastic deformation in a hot-extruded AZ 31 Mg alloy was investigated using a compression test with such parameters as deformation temperature, strain rate. It was observed from true stress-strain curves that twinning involves changes of the flow stresses. In the early stages of deformation at temperatures lower than $200^{\circ}C$, the occurrence of twins resulted in a decrease of the work-hardening rate, which increased drastically at a true strain of -0.05. The evolution of the deformation textures were assessed with the aid of EBSD analyses in terms of the competition between twinning and slip activity.

• Transactions of Materials Processing
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• v.30 no.1
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• pp.43-48
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• 2021

The success of warm forming of Mg alloy sheet is greatly influenced by friction at elevated temperature, depending on the surface treatment of the tool. The tool coating affected the frictional characteristics of AZ31B Mg alloy sheet at elevated and room temperatures. The frictional behavior of the Mg alloy sheet at room temperature was not significantly affected by surface treatment conditions of the tool, but was significantly affected at elevated temperature. When the contact pressure is high, a few surface-treated tools exhibit a higher coefficient of friction than those without surface treatment. It is important to select the surface treatment conditions of the tool in order to ensure appropriate friction during warm forming of Mg alloy sheet.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.4
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• pp.395-400
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• 2009

As the variables affecting the fatigue behavior have uncertainty, the fatigue crack propagation is stochastic in nature. Therefore, the fatigue life prediction is critical for the design and the maintenance of many structural components. In this study, fatigue experiments are conducted on the specimens of magnesium alloy under the different thicknesses of specimen. The effects of specimen thickness on the probability distribution of the fatigue crack propagation life and the crack size are estimated experimentally. The probability distribution of the crack size and the fatigue life for different specimen thicknesses are investigated by Anderson-Darling test and the best fit for those probability distributions are also presented.

• Laser Solutions
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• v.14 no.3
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• pp.12-16
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• 2011

In automotive industry, because of the consideration of fuel economy, lightweight alloys have been adopted and are expected to be extensively used in the future. Magnesium alloys are among the promising materials, due to their lightweight and good mechanical properties. This study is related to the laser weldability of AZ31B magnesium alloy, an all-purpose wrought alloy with good strength and ductility. A 4kW Nd:YAG laser was used to join AZ31B sheet, and the effects of welding parameter on the quality of lap-welded joints were investigated. As a result of this study, the optimal condition was obtained, and the effect of gap distance was also revealed on the porosity control.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.463-466
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• 2005

Restoring ductility or removing residual stresses is a necessary operation when a large amount of cold working is to be performed, such as in a cold-forging or warm forging process. The advantage of annealing temperatures was investigated. After Hydrostatic Extrusion process, extruded materials were annealed at $200^{\circ}C,\;350^{\circ}C,\;450^{\circ}C$ for 1 hour. Microstructure of the annealed material was observed to make an understand about the difference in mechanical properties.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.70-73
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• 2007

The forming characteristics of cup-rod combined extrusion process were investigated with process parameter change. Simultaneous forward rod extrusion and backward cup extrusion was conducted with magnesium alloy, AZ31B. Process parameters such as forward extrusion ratio, backward extrusion ratio, and working temperature were controlled in a specific region and the effects of the parameter change were examined. Surface crack was developed in a certain state of the process parameters combination. The crack-free forming limit of the alloy in the combined process was disclosed by the parameter study. The microstructures of the initial and extruded workpieces were observed.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.5
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• pp.536-543
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• 2009

In this paper the mean stress effects on the probability distribution of the random grown crack size at a specified loading cycle are studied through the fatigue crack propagation tests, which are conducted on the specimens of magnesium alloy under four different stress ratios. Through 80 replicates the probability distributions of the grown crack size are obtained. The goodness-of-fit for probability distributions of the random grown crack size are investigated by Anderson-Darling test and the best fit for those probability distributions is found to be a 3-parameter Weibull distribution. The effects of the mean stress on the probability distribution of the random grown crack size are also estimated.

• Journal of the Korean institute of surface engineering
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• v.52 no.5
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• pp.265-274
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• 2019

Formation behavior of PEO (Plasma Electrolytic Oxidation) films on AZ31 Mg alloy was investigated under application of 310 Hz AC as a function of $Na_3PO_4$ concentration from 0.02 M to 0.2 M. Film formation voltage and in-situ observation of arcs generated on the specimen surface were recorded with time, and surface morphologies of the PEO films were investigated using optical microscopy, confocal scanning laser microscopy and scanning electron microscopy. PEO film formation voltage decreased linearly with increasing $Na_3PO_4$ concentration which is attributed to the increase of solution pH. PEO films were grown uniformly over the entire surface in $Na_3PO_4$ solutions between 0.05 M and 0.1 M. However, non-uniform PEO films with white spots were formed in $Na_3PO_4$ solutions containing more than 0.1 M. Thickness and roughness of PEO films on AZ31 Mg alloy increased linearly with increasing $Na_3PO_4$ concentration and their increasing rates appeared to be much higher under 1 M than above 1 M. The experimental results suggest that phosphate ions can contribute to the formation of PEO films but higher $Na_3PO_4$ concentration more than 1 M results in local damages of PEO films due to repeated generation of white arcs at the same surface site of AZ31 Mg alloy.