• 대한금속재료학회지
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• 제48권3호
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• pp.218-224
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• 2010

Direct copper electroplating on Mg alloy AZ31B was carried out in a traditional pyrophosphate copper bath containing potassium fluoride. Electrochemical impedance spectroscopy and polarization methods were used to study the effects of added potassium fluoride on electrochemical behavior. The chemical state of magnesium alloy in the electroplating bath was analyzed by X-ray photoelectron spectroscopy. Adhesion of the copper electroplated layer was also tested. Due to the added potassium fluoride, a magnesium fluoride film was formed in the pyrophosphate copper bath. This fluoride film inhibits dissolution of Mg alloy and enables to electroplate copper directly on it. A dense copper layer was formed on the Mg alloy. Moreover, this copper layer has a good adhesion with Mg alloy substrate.

• 한국주조공학회지
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• 제32권3호
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• pp.150-156
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• 2012

발포금속은 초경량 재료로서 폐기공과 개기공의 두 가지 형태의 구조를 지니고 있으며 폐기공은 내충격성, 흡음성, 단열성의 기능을 지니고 있고, 개기공은 필터, 생체지지대, 촉매재, 열방출재 등으로 사용되고 있다. 개기공발포재는 삼차원 구조모양으로 프리커서를 이용한 압력정밀주조나 기공입자용출법으로 제조하고 있으나 기공의 크기나 셀의 형상, 두께 등을 조절하기에 어려움이 있다. 이를 해결하기 위하여 환경친화적인 펄라이트를 사용하여 목적하는 크기의 그래뉼을 제조한 후, 용융마그네슘합금을 감압주조법으로 주조하여 그래뉼의 크기로 기공율을 조절하고, 주형의 온도와 압력에 따른 유동의 길이를 측정하였다. 그래뉼 직경이 2.3 $mm{\O}$ 일때에 주형의 온도 $300^{\circ}C$ 이상, 압력이 5000 Pa 이상에서 유동길이 6.5 cm 이상을 얻었다.

• 소성∙가공
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• 제18권4호
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• pp.347-353
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• 2009

The apparent activation energy, the applied stress exponent, and rupture life have been measured from creep experiments over the range of $200^{\circ}C$ to $220^{\circ}C$ and the applied stress range of 64MPa to 94MPa. The materials were used AZ31 magnesium alloys treated by plasma electrolytic oxidation of $20{\mu}m$ and $40{\mu}m$ at surface to investigate the its influence on creep behavior, and creep tests were carried out under constant applied stress and temperature. The experimental results showed that the dipper the thickness of surface treatment the higher the activation energy and stress exponent. And the higher temperature and applied stress, the lower stress exponent and activation energy, respectively. Also the dipper the thickness of surface treatment the longer creep rupture time.

• 한국기계가공학회지
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• 제11권2호
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• pp.34-39
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• 2012

In this study, the friction welding experiment was performed by using the design of experiment. And the signal data acquired by acoustic emission sensor were analyzed to predict the tensile strength of friction welding part at friction welding process for AZ31 magnesium alloy. A dimensionless coefficient($\phi_{AE}$), which consisted in the square of AE rms and variance, was defined as the characteristic of friction welding and the prediction equation was obtained by using linear regression. As the result of analysis, it was seen that the correlation between predicted and measured values became very close and on-line prediction of the ensile strength was possible in friction welding part.

• 소성∙가공
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• 제17권2호
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• pp.97-101
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• 2008

Unique constitutive behavior of magnesium alloys as one of hexagonal close packed(hcp) metals has been implemented into the commercial finite element program ABAQUS. The constitutive equations can represent asymmetry in tension-compression yield stresses and flow curves. For the verification purpose, the springback of AZ31B magnesium alloy sheet was measured using the unconstrained cylindrical bending test proposed in Numisheet'2002 benchmark committee. Besides the developed constitutive models, the isotropic models based on tensile and compressive properties were also considered for comparison purpose. The predicted results by the finite element analysis and corresponding experiments showed enhanced prediction capability in springback analysis.

• Journal of Welding and Joining
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• 제31권6호
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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.

• 한국자동차공학회논문집
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• 제13권3호
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• pp.186-192
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• 2005

The apparent activation energy Qc, the applied stress exponent n, and rupture life have been determined from creep test results of AZ31 Mg alloy over the temperature range of 200$^{\circ}C$ to 300$^{\circ}C$ and the stress range of 23.42 MPa to 93.59 MPa, respectively, in order to investigate the creep behavior. Constant load creep tests were carried out in the equipment including automatic temperature controller with data acquisition computer. At the temperature of $200^{\circ}C{\sim}220^{\circ}C$ and under the stress level of 62.43~93.59 MPa, and at around the temperature of $280^{\circ}C{\sim}300^{\circ}C$ and under the stress level of 23.42~39.00 MPa, the creep behavior obeyed a simple power-law relating steady state creep rate to applied stress and the activation energy fur the creep deformation was nearly equal to that of the self diffusion of Mg alloy including aluminum From the above results, at the temperature of $200^{\circ}C{\sim}220^{\circ}C$ the creep deformation for AZ31 Mg alloy seemed to be controlled by dislocation climb but controlled by dislocation glide at $280^{\circ}C{\sim}300^{\circ}C$ .And relationship beween rupture time and stress at around the temperature of $200^{\circ}C{\sim}220^{\circ}C$ and under the stress level of 62.43~93.59 MPa, and again at around the temperature of $280^{\circ}C{\sim}300^{\circ}C$ and under the stress level of 23.42~39.00 MPa, respectively, appeard as fullow; log$\sigma$=-0.18(T+460)(logtr+21)+5.92, log$\sigma$ = -0.25(T+460)(logtr+21)+8.02 Also relationship beween rupture time and steady state creep rate appears as follow; ln$\dot$ =-0.881ntr-2.45

• 대한기계학회논문집A
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• 제36권12호
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• pp.1675-1682
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• 2012

경량화는 대기오염과 자원고갈의 측면에서 매우 중요하게 인식되고 있어, 많은 자동차용 부품이 Al 및 Mg 합금으로 대체되었으며, 관련 연구가 지속적으로 증가하고 있다. 그러나 Mg 합금은 Al 합금에 비해 높은 재료비와 난성형성으로 인한 낮은 생산성 때문에 제한적으로 적용되고 있다. 본 연구에서는 FEA를 이용하여 자동차 범퍼 백 빔용 관재에 대한 공정조건을 분석하였으며, 생산성을 향상시킬 수 있는 방법을 확립하였다. 물성치 확보를 위해 물성시험을 수행하였으며, 소성변형 중 발생하는 열 관련 물성을 정의하기 위하여 단순형상에 대한 실험과 해석을 수행하였다. 이후 온도조건 및 램 속도를 고려하여 제품에 대한 해석을 수행하였다. 이를 통하여 압출공정조건을 확립하였으며, 표면결함이 없는 제품을 성형하는데 성공하였다.

• 소성∙가공
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• 제23권4호
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• pp.238-243
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• 2014

Recently, magnesium alloys have been widely used in the automotive, aerospace and electronics industries with the advantages of high specific strength, excellent machinability, high electrical conductivity, and high thermal conductivity. Deep drawn magnesium alloys not only meet the demands environmentally and the need for lighter products, but also can lead to remarkably improved productivity and more rapid qualification of the product The current study reports on a failure prediction procedure using finite element modeling (FEM) and a ductile fracture criterion and applies this procedure to the design of a deep drawing process. Critical damage values were determined from a series of uniaxial tensile tests and FEM simulations. They were then expressed as a function of strain rate and temperature. Based on the plastic deformation histories obtained from the FEM analyses of the warm drawing process and the critical damage value curves, the initiation time and location of fracture were predicted. The proposed method was applied to the process design for fabrication of a Mg automotive compressor case and verified with experimental results. The final results indicate that a Mg case part 39% lighter than an Al die casting part can be produced without any defects.

• Corrosion Science and Technology
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• 제17권1호
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• pp.30-36
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• 2018

The high rate of corrosion of magnesium alloys makes it limited for industrial applications. Therefore, surface treatment is required to enhance their corrosion resistance. In our study, a chemical conversion coating for protecting the corrosion of the magnesium alloy, AZ31B, was prepared by using a phosphate-permanganate solution. The chemical conversion coating had a limited protection ability due to defects arising from cracks and pores in the coating layer. The sol-gel coating was prepared by using trimethoxymethylsilane (MTMS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) as precursors, and aluminum acetyl acetonate as a ring opening agent. The corrosion protection properties of sol-gel and conversion coatings in 0.35wt% NaCl solution were measured by the electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization test. The EIS results indicated that the resistance of the chemical conversion coating with the sol-gel coating was significantly improved through the sol-gel sealed phosphate-permanganate conversion coating. The results of the potentiodynamic polarization test revealed that the sol-gel coating decreased the corrosion current density ($I_{corr}$). The SEM image showed that the sol-gel coating sealed conversion coating and improved corrosion protection.