• 소성∙가공
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• 제26권3호
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• pp.168-173
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• 2017

A new sheet metal forming process, called flexibly reconfigurable roll forming (FRRF), is expected to resolve the economical limitation of the existing 3D curved sheet metal forming processes. The height-controllable guides and a couple of flexible rollers are utilized as the forming tool. Recently, as the 3D curved sheet metal is increasingly demanded in various fields, the application of FRRF to diverse materials is necessary. In addition, the formability comparison of several materials is needed. Therefore, in this study, we investigated the applicability of FRRF for different materials such as aluminum, magnesium, and copper alloys, and also the formability of these materials was compared using FRRF. The numerical simulation was conducted using ABAQUS, the commercial software, and the experiments were carried out using an FRRF apparatus to validate the simulation results. Finally, the applicability of FRRF for the chosen materials and the formability of these materials on FRRF process were confirmed by comparing the simulation and experimental results.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.534-538
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• 2002

Dissimilar friction stir welding of aluminum (AI) alloy 1050 and magnesium (Mg) alloy AZ31 was successfully done in the limited welding parameters. The dissimilar weld showed good quality and facility compared to conventional fusion weld. Transverse cross section perpendicular to the welding direction had no defects. The weld was divided into base material of Al alloy, an irregular shaped stir zone and base material of Mg alloy. The irregular shaped stir zone was roughly located around the initial weld center. The weld interface near plate surface shifted from initial weld centerline to the advancing side. Hardness profile of the weld was heterogeneous, and the hardness value of the stir zone was raised to about 150 Hv to 250 Hv. The mixed phase was identified to intermetallic compound $Mg_{17}$Al$_{12}$ using x-ray diffraction method, energy dispersive x-ray spectroscopy (EDX) and electron probe micro analysis (EPMA). The formation of intermetallic compound $Mg_{17}$Al$_{12}$ during FSW causes the remarkable increase in hardness value in the stir zone.one.

• Advances in materials Research
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• 제4권2호
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• pp.77-85
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• 2015

The influence of rare earth lanthanum (La) on solidification cooling range, microstructure of aluminum-magnesium (Al-Mg) alloy and mechanical properties were investigated. Five kinds of Al-Mg alloys with rare earth content of La (i.e., 0, 0.5, 1.0, 1.5 and 2.0 wt.%) were prepared. Samples were either slowly cooled in furnace or water cooled. Results indicate that the addition of the rare earth (RE) La can significantly influence the solidification range, the resultant microstructure, and tensile strength. RE La can extend the alloy solidification range, increase the solidification time, and also greatly improve the flow performance. The addition of La takes a metamorphism effect on Al-Mg alloy, resulting in that the finer the grain is obtained, the rounder the morphology becomes. RE La can significantly increase the mechanical properties for its metamorphism and reinforcement. When the La content is about 1.5 wt.%, the tensile strength of Al-Mg alloy reaches its maximum value of 314 MPa.

• 한국산학기술학회논문지
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• 제18권8호
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• pp.1-7
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• 2017

본 논문은 퍼스널 모빌리티에 사용되는 360 Wh급 리튬이온 배터리 팩의 성능 및 안정성 확보를 위하여 리튬이온 배터리 팩의 열전달 특성에 관하여 상용수치해석 프로그램인 ANSYS v17.0의 CFX를 이용하여 수치적으로 연구하였다. 이를 위하여 퍼스널 모빌리티에 사용되는 360 Wh급 리튬이온 배터리 팩의 배터리 셀 배열을 4가지 경우로 변경하고, 배터리 셀 홀더에 사용되는 재질과 배터리 팩 케이스에 사용되는 재질을 각각 Polypropylene, Aluminium, Magnesium alloy로 변경하였다. 그 결과 배터리 평균 온도는 배터리 셀 배열이 Model 2 일 때 가장 낮게 예측되었으며, 배터리 셀 홀더와 배터리 팩 케이스 재질 변경에 따른 배터리 평균 온도는 대부분의 경우 Aluminium 일 때 가장 낮게 예측되었다. 퍼스널 모빌리티에 사용되는 360 Wh급 리튬이온 배터리 팩의 열전달 성능은 배터리 셀 배열과 배터리 팩 케이스 재질에 많은 영향을 받았으며, 배터리 셀 배열 Model 2와 배터리 팩 케이스 재질이 Aluminium 일 때 가장 높았다.

• 동력기계공학회지
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• 제9권4호
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• pp.96-101
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• 2005

Magnesium alloys have been widely used for many structural components of automobiles and aircraft because of high specific strength and good cast ability in spite of hexagonal closed-packed crystal structure of pure magnesium. In this study, uniaxial tension tests at high temperature and creep tests are done in order to investigate the characteristics of high temperature and mechanisms for creep deformation of AZ31 Mg alloy. Yield stress and ultimate tensile stress decreased with increasing temperature, but elongation increased from results of uniaxial tension test at high temperature. The apparent activation energy Qc, the applied stress exponent n and rupture life have been determined during creep of AZ31 Mg alloy over the temperature range of 473K to 573K and 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, whose data are sent to computer. At around the temperature of $473K{\sim}493K$ and under the stress level of $62.43{\sim}93.59%MPa$, and again at around the temperature of $553K{\sim}573K$ and under the stress level of $23.42{\sim}39.00MPa$, the creep behavior obeyed a simple power-law relating steady state creep rate to applied stress and the activation energy for the creep deformation was nearly equal, respectively, and a little low to that of the self diffusion of Mg alloy including aluminum. Also rupture surfaces at high temperature have had bigger dimples than those at lower temperature by SEM.

• 한국주조공학회지
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• 제14권3호
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• pp.240-247
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• 1994

TiC particulate reinforced magnesium matrix composites were fabricated by melt stirring method. The effect of alloying elements on TiC particulate dispersion into molten magnesium and mechanical properties were investigated. The incorporation time is defined as the time required for dispersion of solid particles into molten metal. The incorporation time of TiC particles into molten pure magnesium was remarkably shorter and the particulated dispersion was more uniform than that of pure aluminum which was reported previously. The incorporation time was, prolonged by the addition of Al, Bi, Ca, Ce, Pb, Sn or Zn. The tensile strength increased and elongation decreased by the addition of Cu or Sn into the matrices and composites. Although, the tensile strength of the matrices and composites increased by alloying with Ca or Ce, the maximum elongation was observed at a content of about 1% for the matrices. By alloying with Zn, the tensile strength increased for the matrices and composites, but the elongation of the matrices increased. The pure magnesium and its alloy matrix composites reinforced with 20vol% TiC have the tensile strength of about 400MPa. This value is compared with the tensile strength of SiC whisker reinforced magnesium matrix composites fabricated by liquid infiltration method at the same volume fraction. There fore, the melt strirring method which has the advantages of simple process is considered to be efficient in fabricating magnesium matrix composites.

• 소성∙가공
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• 제25권3호
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• pp.155-160
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• 2016

Magnesium(Mg) alloys have been evaluated as replacements for steel or aluminum parts in the automobile industry because of the fuel economy they can provide through reducing weight. The application of Mg alloys has been limited due to its low formability at room temperature, which results from a small number of active slip systems. In the current study, an extruded TAZ711(Mg-7Sn-1Al-1Zn) alloy was warm forged into an automotive control arm to evaluate its formability at various forging temperature. Warm forging was conducted at temperatures of 200, 250, 350 and 450℃. Static strength evaluation was performed on the as-forged specimen at 250℃. The results showed good static strength.

• 한국군사과학기술학회지
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• 제8권3호
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• pp.101-110
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• 2005

In this paper, the experiments have been conducted to measure the residual velocity for 3.5g steel ball perforating light weight metal plates of aluminum alloy and magnesium alloy. Non-contact electro-magnetic sensors were used to measure the velocity of steel ball before/after perforating plates. The thicknesses of specimens used were about 2.8mm and 4.8mm. The impact velocities of steel ball were from 662m/s to 3594m/s. With same conditions, numerical analysis using Autodyn 2D has been conducted. The results of numerical analysis corresponded with those of experiments. Also, It is suggested that the difference between the residual velocity of experiment or numerical analysis and that of THOR experimental equation of BRL grew smaller as the impact velocity were increased.

• 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.

• Journal of Welding and Joining
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• 제29권4호
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• pp.80-84
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• 2011

In the 5xxx series Al-Mg alloy, magnesium addition can increase the strength of aluminum alloy by solid solution strengthening but it has a relatively low melting and boiling temperature. During full -penetration laser welding of the Al-Mg alloys, its low boiling point and high vapor pressure brings about the spiky humping bead on the bottom side. Under back-side shielding, the spiking of back bead can be reduced but it restraints the process flexibility. In this study, a square pulse waveform modulation was employed to stabilize keyhole and back bead surface without back-side shielding. By using an experimental design, the bead shapes were evaluated for various process parameters such as the focal position, welding velocity and waveform parameters and the smooth back bead shape could be achieved.