• 소성∙가공
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• 제17권7호
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• pp.466-472
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• 2008

In this paper, tension tests and formability tests are performed to construct a database related to mechanical properties and the formability of the AZ31B Mg alloy sheet. A forming test with a hemi-spherical punch is conducted at varying temperatures to establish a forming limit diagram. In order to verify the applicability of the analysis using the conventional flow hardening model, a finite element analysis is performed on the hemi-spherical punch forming process and the results are compared with experimental ones. The study investigates problems involving a computational analysis that does not consider flow softening of the magnesium alloy at elevated temperatures.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.366-369
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• 2008

In this paper, tension tests and formability tests are performed to construct a database related to mechanical properties and the formability of the AZ31B Mg alloy sheet. A forming test with a hemi-spherical punch is conducted at varying temperatures to establish a forming limit diagram. In order to verify the applicability of the analysis using the conventional flow hardening model, a finite element analysis is performed on the hemi-spherical punch forming process and the results are compared with experimental ones. The study investigates problems involving a computational analysis that does not consider flow softening of the magnesium alloy at elevated temperatures.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.231-234
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• 2005

The high temperature deformation behavior of AZ 31 Mg alloy was investigated by designing a back propagation neural network that uses a gradient descent-learning algorithm. A neural network modeling is an intelligent technique that can solve non-linear and complex problems by learning from the samples. Therefore, some experimental data have been firstly obtained from continuous compression tests performed on a thermo-mechanical simulator over a range of temperatures $(250-500^{\circ}C)$ with strain rates of $0.0001-100s^{-1}$ and true strains of 0.1 to 0.6. The inputs for neural network model are strain, strain rate, and temperature and the output is flow stress. It was found that the trained model could well predict the flow stress for some experimental data that have not been used in the training. Workability of a material can be evaluated by means of power dissipation map with respect to strain, strain rate and temperature. Power dissipation map was constructed using the flow stress predicted from the neural network model at finer Intervals of strain, strain rates and subsequently processing maps were developed for hot working processes for AZ 31 Mg alloy. The safe domains of hot working of AZ 31 Mg alloy were identified and validated through microstructural investigations.

• Journal of Welding and Joining
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• 제22권3호
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• pp.56-61
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• 2004

Friction stir weldability of AZ31B Mg alloy was studied using microstructural observation and mechanical tests. Defect free joints was obtained under the condition of 2000rpm-100mm/min. In TMAZ, a lot of twin deformation were observed due to the mechanical effect of the FSW tool and thus relatively high hardness was obtained. In SZ, the twin deformation was disappeared by recovery and the hardness decreased because the. grain structure was coarsened by dynamic recrystallization and grain growth. The Al-Mn precipitates were observed throughout the joint regions. On the other hand, $$\beta$-Mg_{17}Al_{12}$ intermetallic compounds were not observed in either of the zone. The joint efficiency was about 80% and the impact value of the joint was almost equal to that of base metal.

• 소성∙가공
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• 제23권8호
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• pp.495-500
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• 2014

Magnesium alloys are currently expected to be widely used for weight reduction of cars and as high efficient materials in the automotive and electronics industries. Although the specific strength of magnesium is excellent, it cannot be easily formed at room temperature due to its HCP structure. However in order to improve the formability of magnesium, it is necessary to investigate its formability in the warm temperature range. In the current study, the aim was to add to the magnesium property database so that the mass production of a magnesium car body can be accomplished. Warm tensile tests were conducted and the forming limit diagram was determined to confirm formability characteristics of magnesium AZ31B alloy sheet. In addition the bending formability and the magnesium damping capacity were evaluated for AZ31B and compared to SPRC440E which is a sheet steel used for car bodies.

• Corrosion Science and Technology
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• 제5권2호
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• pp.77-83
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• 2006

The plasma electrolytic oxidation (PEO) process is a relatively new surface treatment technique that produces a chemically stable and environment-friendly electrolytic coating that can be applied to all types of magnesium alloys. In this study, the characteristics of oxide film were examined after coating the extruded AZ31 alloy through the PEO process. Hard ceramic coatings were obtained on the AZ31 alloy by changing the coating time from 10min to 60min. The morphologies of the surface and the cross-section of the PEO coatings were examined by scanning electron microscopy and optical microscopy, and the thickness of the coating was measured. The X-ray diffraction pattern of the coating shows that the coated layer consists mainly of the MgO and $Mg_2SiO_4$ phases after the oxidation reaction. The hardness of the coated AZ31 alloy increased with increasing coating time. In addition, the corrosion rates of the coated and uncoated AZ31 alloys were examined by salt spray tests according to ASTM B 117 and the results show that the corrosion resistance of the coated AZ31 alloy was superior to that of the un-coated AZ31 alloy.

• Corrosion Science and Technology
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• 제18권6호
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• pp.243-252
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• 2019

The pitting corrosion and inhibition studies of AZ31B magnesium alloy were investigated in the alkaline solution (pH12) with chloride and inhibitors. The corrosion behavior of passive film with/without Cl^- in the alkaline electrolyte were conducted by polarization curve and immersion tests in the presence of various additives (inhibitors) to clarify the inhibition efficiency of pitting corrosion at higher potential region. Critical concentration of pitting corrosion for Mg alloy was evaluated with 0.005 M NaCl in 0.01 M NaOH on the anodic polarization behavior. Critical pitting of AZ31B Mg alloy in 0.01 M NaOH is a function of chlorides; E_pit = - 1.36 - 0.2 log [Cl^-]. When the Sodium Benzoate (SB) was only used as an inhibitor, a few metastable pits developed on the Mg surface by an immersion test despite no pitting corrosion on the polarization curve meaning that adsorption of SB on the surface is insufficient protection from pitting corrosion in the presence of chloride. The role of SB and Sodium Dodecylbenzenesulfonate (SDBS) inhibitors for the Mg alloy surface in the presence of chloride was suppressed from pitting corrosion to co-adsorb on the Mg alloy surface with strong formation of passive film preventing pitting corrosion.

• 소성∙가공
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• 제16권6호
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• pp.447-451
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• 2007

The springback characteristics of AZ31B magnesium alloy sheet was investigated in OSU draw/bend test Springback is the elastically-driven change of shape of a part after forming and it should be estimated and controlled to manufacture more precise products in sheet forming. Magnesium alloy sheets have unique mechanical properties such as high in-plane anisotropy/asymmetry of yield stress and hardening response. So, there will be a difference in the prediction of springback with symmetric mechanical properties for magnesium alloy sheets. In this work, the Strip draw/bend tests were conducted with various conditions - die radius, sheet thickness and controlled tensile force and the tendency of springback angle was observed from the tests.

• 열처리공학회지
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• 제21권6호
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• pp.293-299
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• 2008

In order to provide with fundamental data of the wrought Mg alloy for press forging, the effect of annealing temperature on the microstructure, texture development and tensile properties is studied in a commercial AZ31B Mg alloy sheet. Basal texture i.e. $(0001){\pm}5^{\circ}$[21$\bar{3}$0] is developed in a commercial AZ31B Mg sheet, and the texture is not changed considerably by annealing over $400^{\circ}C{\times}30min$, while (10$\bar{3}$0) component with high intensity can be observed due to abnormal grain growth. When the sheet is tensile-deformed with RD, $45^{\circ}$ and TD directions at room temperature, fracture strains are given by 25.8, 21.4 and 11.9% in the order of RD, $45^{\circ}$ and TD directions, respectively. With increasing annealing temperature up to $450^{\circ}C{\times}30min$, little change in mean grain size can be revealed by annealing below $300^{\circ}C{\times}30min$ but an abnormal grain growth, where some grains become significantly coarser than the rest, occurs by annealing above $400^{\circ}C{\times}30min$. The maximum tensile strain of around 25% is obtained by annealing below $300^{\circ}C{\times}30min$, but it is abruptly decreased to 16% by annealing above $400^{\circ}C{\times}30min$ owing to intergranular fracture of abnormal grown grains.

• 대한금속재료학회지
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• 제49권3호
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• pp.270-274
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• 2011

Plasma electrolytic oxidation (PEO) treatment was performed on squeeze cast AZ31 alloy and $Al_{18}B_4O_{33}w/AZ31$ composite. Scanning electron microscope (SEM) was employed to characterize the surface morphology and cross-section microstructure of the coating. The phase structures of the PEO coating were analyzed by X-ray diffraction (XRD). The corrosion resistance of the PEO coating was evaluated by electrochemical method. The results showed that the $Al_{18}B_4O_{33}$ whisker on the surface of the composite was decomposed and $MgAl_2O_4$ was formed in the PEO coating layer of $Al_{18}B_4O_{33}w/AZ31$ composite during PEO treatment. As a result, the electrochemical corrosion potential of the PEO coated $Al_{18}B_4O_{33}w/AZ31$ composite was increased compared with that of AZ31 alloy.