• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.193.2-193.2
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• 2016

본 연구에서는 탄산이온이 포함된 수용액에서 규산나트륨의 농도가 AZ31 마그네슘 합금의 플라즈마전해산화 피막형성에 미치는 영향에 대해 알아보았다. 다양한 농도의 규산나트륨 용액에서 DC와 펄스전류를 인가하여 플라즈마전해산화피막을 형성하였으며, 형성된 피막의 surface roughness와 thickness를 분석하였다. 탄산 이온이 포함된 수용액에서 플라즈마전해산화 피막의 형성전압은 규산나트륨의 농도가 높아질수록 높아지는 것으로 나타났다. 하지만 탄산이온이 존재하지 않은 규산나트륨 용액에서의 플라즈마전해산화 피막 형성전압보다 더 낮은 값을 나타내었다. 탄산 이온이 포함된 수용액에서 규산나트륨의 농도가 높아질수록 플라즈마전해산화 피막의 surface roughness와 thickness는 증가하였으며, DC와 펄스전류 모두에서 더 밝은 색상의 균일한 산화피막을 형성할 수 있었다.

• 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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.377-380
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• 2005

In this study, the experiments of warm deep drawing were done with heated die, and with heated die and cooled punch in order to investigate the formability of ZA31 magnesium sheet alloy of warm deep drawing. For this, warm deep drawing experiments were executed under various temperature, punch velocity and blankholder force. The results of warm deep drawing with heated die showed that fracture occurred punch part at punch velocity of 75mm/min and punch stroke of 10mm under temperature of $100^{\circ}C\~250^{\circ}C$, but did not occure under temperature of $275^{\circ}C\~400^{\circ}C$. And fracture at punch stroke of 25mm did not occurre at punch part under punch velocity of 30mm/min and $250^{\circ}C$, but occured under punch velocity of 75 and 125 mm/min. Also the results of warm deep drawing with heated die and cooled punch showed that the temperature happening maximum height under punch velocity of 10-100mm/min was $225-250^{\circ}C$. And necking occurred at punch shoulder under $20\~150^{\circ}C$, but at die wall under $200\~300^{\circ}C$.

• Design & Manufacturing
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• v.10 no.1
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• pp.12-18
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• 2016

Although magnesium alloy has received much attention to date for its lightweight and high specific strength, their applications are impeded by the low formability which is caused by the hexagonal crystal structure at room temperature. In general, equal-channel angular extrusion(ECAE) is recognized as one of the attractive severe plastic deformation techniques where the processed bulk metals generally achieve ultrafine-grained microstructure leading to improved physical characteristics and mechanical properties. ECAE process has several parameters such as angle of die, process temperature, process route and speed. During ECAE process of Mg alloy, these parameters has great influence on the extrudability and the mechanical properties of alloy. The aim of this study is to estimate the influences of process conditions on the formability of AZ31 and AZ31-CaO alloys. Mg alloys are processed through ECAE at elevated temperatures using three types of die with channel angle of $90^{\circ}$, $110^{\circ}$, $135^{\circ}$ using route $B_c$, respectively. This study discusses the feasibility of using ECAE to improve both formability and strength on magnesium alloys by comparative analyzing the mechanical properties and microstructural evolution in each condition.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.6
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• pp.93-98
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• 2005

The purpose of this study is to confirm the improvement of formability of AZ31 magnesium alloy sheet by using local heating and cooling technique. For this, the experiments of warm deep drawing were done under the temperatures of $100^{\circ}C\~400^{\circ}C$, and the punch velocity of 10, 100mm/min. Also FE analysis under the temperatures of blankholder and die of $150^{\circ}C,\;225^{\circ}C\;and\;300^{\circ}C$ for tools(holder and die) was executed with considering heat teansfer. From the results, the formability of AZ31 magnesium alloy, espicially the temperatures of $225^{\circ}C\~250^{\circ}C$ for tools(holder and die)improved remarkably. And the experiments and simulations showed that necking under room temperature for tools occured under the part of punch shoulder while at $300^{\circ}C$ for tools, at the part of die shoulder.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.378-382
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• 2008

Since the sheet metal forming of Mg alloy is perform at elevated temperature, the effect of strain rates related with the forming temperature and forming speed and R-value is very important factor for formability and forming limits and deep drawing. It is investigated that the effect of material properties such as various temperature, forming speed and strain rates on formability and R-value of Mg alloy sheet in round cup deep drawing. Therefore, the investigation for process variables is necessary to improve formability and forming limits and deep drawing. Also, the effects of strain rate and drawbility were studied by the experiment. The temperature, forming speed, and strain rates and R-value are investigated. Forming of Mg alloy takes consider into temperature, proper forming speed and strain-rate and R-value the formed parts were good without defects for forming limits and deep drawing.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.349-353
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• 2008

A fundamental study on warm incremental forming of a magnesium alloy sheet has been carried out. In order to enhance the incremental formability of the magnesium alloy sheet, a local heating device was newly designed and manufactured. Through the incremental forming tests of AZ31 under various forming conditions, the effects of process parameters such as the temperature, feeding depth per cycle, and inclination angle on the incremental formability of AZ31 were investigated. In addition, conventional FLDs at elevated temperatures were constructed experimentally and applied to predict the forming failure.

• Transactions of Materials Processing
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• v.19 no.7
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• pp.416-422
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• 2010

The $\{10\bar{1}2\}$ twinning characteristics, such as active twin variants, volume fraction of twins with strain, twin morphology, twin texture and angle relationship between twins, were dependent on the activation mode (i.e., tension parallel to the caxis or compression perpendicular to the c-axis). The selection criterion of active twin variants was governed by the Schmid law. This activation of selected twin variants depending on the activation mode consequently caused a totally different plastic deformation behavior in two activation modes. The differences in the deformation characteristics, such as flow stress and work hardening rate, between both activation modes were explained in relation with activation stresses for slips and twinning, relative activities of twinning and slips during plastic deformation, grain refining effect by twin boundaries (Hall-Petch effect), and twinning-induced change in activities of slips.

• 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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• 2005.05a
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• pp.69-72
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• 2005

The crystal structure of magnesium is hexagonal close-packed (HCP), so its formability is poor at room temperature. But formability is improved in high temperature with increasing of the slip planes. Purpose of this paper is to know about the mechanical properties of magnesium alloy (AZ31B), before warm and hot forming process. The mechanical properties were defined by the tension and compression tests in various temperature and strain-rate. As the temperature is increased, yield${\cdot}$ultimate strength, K-value, work hardening exponent (n) and anisotropy factor (R) are decreased. But strain rate sensitivity (m) is increased. As strain-rate increased, yield${\cdot}$ultimate strength, K-value, and work hardening exponent (n) are increased. Also, microstructures of grains fine away at high strain-rate. These results will be used in simulations and manufacturing factor for warm and hot forming process.