• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.142-145
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• 2008

A finite element analysis has been conducted to simulate direct/indirect extrusion process for AZ31 Mg alloy at various ram and die speeds. Uniaxial compression test on AZ31 Mg alloy was carried out at various strain rates and temperatures and the result was used as input data fur finite element analysis. It was found that ram speed affects the distribution of dead zone area during direct extrusion. The inhomogeneous temperature and strain distributions through the thickness direction can be simulated under the various extrusion process conditions.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.10
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• pp.77-83
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• 2002

Magnesium alloys casting are gaining increased acceptance in the automotive and electronic industeries and die casting is the most efficient method of manufacturing such mass produced parts. This study has been investigated the microstructures and mechanical properties of Mg-9Al-lZn alloy fabricated by die casting process for development of air bag case. The microstructure of die casted specimen were composed of pro-eutectic magnesium solid solution and $\beta$(Mg17Al12) precipitates. The tensile strength of as-fabricated Mg-9Al-lZn alloy revealed 231.4MPa. It was found that Mg-9Al-lZn alloy have good corrosion resistance in electrochemical polarization test.

• Journal of Korea Foundry Society
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• v.3 no.4
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• pp.256-261
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• 1983

In this study, the variations of tensile strength and yield strength of Al-20% Si alloy were studied. Copper, magnesium and nickel as alloying elements added from 1% to 3% respectively. The temperature range was from room temperature to $350^{\circ}C$. The refinement of primary silicon crystal was treated with phosphorous addition. The results obtained are as follows: 1. Tensile strnegth and yield strength showed more increased strength in refining treated alloy than that of in nonrefining alloy at elevated temperature. 2. Tensile strength and yield strength were increased with the contents of copper. Tensile strength showed the maximum at $150^{\circ}C$, but yield strength was decreased with increasing temperature. 3. The effect of magnesium addition on tensile strength and yield strength showed the maximum at 1% addition and $150^{\circ}C$. 4. Tensile strength and yield strength showed a slight increase with the content changes of nickel and they were decreased with increasing temperature.

• Journal of Surface Science and Engineering
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• v.50 no.1
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• pp.42-45
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• 2017

The magnesium-base AZ61 alloy was cast while adding 1% CaO powder into the melt. It was hot extruded, and oxidized at $550-650^{\circ}C$ in air in order to study its microstructure and oxidation behavior. Initially added CaO powder reacted with Al in the melt to $Al_2Ca$ particles that aligned along the extrusion direction. The formed $Al_2Ca$ particles increased the oxidation resistance through forming the superficial CaO scale at the upper part of the thin MgO oxide scale.

• Journal of Surface Science and Engineering
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• v.50 no.6
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• pp.432-438
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• 2017

AZ91D casting alloy requires an advanced plasma anodizing processing because large amount of defects are liable to generate during anodization. In this study, plasma electrolytic oxidation (PEO) of AZ91D Mg alloy was conducted by the application of either constant voltage or current using a pulse mode and its effects on pore formation, surface roughness and corrosion resistance were investigated. The PEO films showed a three-layer structure. The PEO film thickness was found to increase linearly with voltage. The surface roughness, Ra, ranged between $0.2{\mu}m$ and $0.3{\mu}m$. The corrosion resistance increased from RN 3.5 to 9.5 by the PEO treatment when evaluated according to the 72 hour salt spray test. The PEO-treated surface exhibited higher pitting potential than the raw material.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.516-521
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• 2002

A study was carried out to grow an understanding of the microstructural development of friction stir welds on an AZ91D magnesium alloy, and to evaluate the mechanical properties of the welds. AZ91D plates with the thickness of 4mm were used, and the microstructural development of the weld zone was investigated using optical and scanning electron microscopes. Square butt welding joint with good quality was obtained at the conditions of under 187mm/min of travel speed with 1100 to 1250 rpm of tool rotation speed. The microstructure within the weld region consisted of fine equiaxed grains with no evidence of the original dendritic structure. The hardness tests showed slightly increased harness in the weld region, and the minimum hardness measured is in that of the parent material. Tensile strength of the weld zone was remarkably improved due to very fine recrystallized structure. XRD pattern of weld zone revealed the removal of $\beta$ intermetallic compounds, $Mg_{17}$Al$_{12}$, which had been distributed in the base metal.l.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.2 no.2
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• pp.84-90
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• 2003

Magnesium alloys have been paid attention In automotive and industries as lightweight materials, and with these materials it has been attempted at deep drawing process for assessment of formability of sheet metal. For warm deep drawing process with a local heating and cooling technique, both die and blank holder were heated at warm temperature while the punch was kept at room temperature by cooling water. Warm deep-drawing process with considering heat transfer was simulated by finite element method to investigate the improvement of deep-drawability and temperature distribution of Mg alloy sheet. The effect of sham rate sensitivity index on the deformation profile was considered in this work and the simulation results revealed that considering heat transfer is very effective for deep-drawability of Mg alloy. The deformed blank In considering heat transfer was drawn successfully without any localized thinning and the cup height is higher in contrast to results of simulations in considering no heat transfer.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.73-77
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• 2005

In this work, the influences of tool temperature on the formability of AZ31 sheet material in warm deep drawing processes of square cup were investigated. Deep drawing tests under different tool temperatures for magnesium alloy sheet at elevated temperature $250^{\circ}C$, where AZ31 sheet shows a good formability, and FE analyses were carried out. The successfully formed part without any defects was obtained when temperature of tool was over $100^{\circ}C$ while the fracture was occurred at the corner of the square cup below $100^{\circ}C$. It is shown that lower temperature of tool than that of magnesium sheet causes the temperature drop of the material by heat transfer and thus Interrupts the dynamic recrystallization of it. Therefore, in order to obtain successful part of magnesium alloys, it is necessary that the tool temperature is limited to the same or slightly lower temperature than sheet material.

• Korean Journal of Metals and Materials
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• v.48 no.8
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• pp.724-729
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• 2010

The effect of potassium permanganate ($KMnO_4$) in an electrolyte on the corrosion performance of magnesium alloy coated by micro-arc oxidation (MAO) has been investigated in this study. For this purpose, MAO coating was carried out on the present sample under AC condition in an alkaline silicate electrolyte with and without $KMnO_4$. Irrespective of the addition of $KMnO_4$, it was found from structural observation that the ceramic coating layers consisted of inner and outer layers. In the sample processed in the electrolyte with $KMnO_4$, the outer layer became dense and even contained a number of $Mn_2O_3$ atoms, resulting in high corrosion resistance. Based on the results of a potentiodynamic polarization test, it was confirmed that the coating layer formed in the electrolyte with $KMnO_4$exhibited better corrosion resistance than that without $KMnO_4$. The high corrosion resistance of the MAO-treated magnesium alloy was explained in relation to the equivalent circuit model.

• Journal of Surface Science and Engineering
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• v.42 no.3
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• pp.109-115
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• 2009

Magnesium is one of the lightest metals, and magnesium alloys have excellent physical and mechanical properties such as high stiffness/weight ratios, good castability, good vibration and shock absorption. However their poor corrosion resistance, wear resistance, hardness and so on, have limited their application. To improve these defects, many techniques are developed. Micro arc oxidation(MAO) is a one of the surface treatments under anodic oxidation in which ceramic coating is directly formed on the surface of magnesium alloy. In this study, the characteristics of anodic film were examined after coating the AZ31B magnesium alloy through the MAO process. MAO was carried out in potassium hydroxide, potassium fluoride, and various concentration of sodium silicate in electrolyte. The morphology and chemical composition of the coating layer were characterized by SEM, XRD, EPMA and EDS. The hardness of anodic films was measured by micro-vickers hardness tester. As a result, the morphology and composition of anodic film were changed by concentration of sodium silicate. Thickness and Si composition of anodic film was increased with increasing concentration of sodium silicate in electrolyte. The hardness of anodic film was highly increased when the concentration of sodium silicate was above 40 g/l in electrolyte.