• Journal of Korea Foundry Society
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• v.32 no.2
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• pp.75-80
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• 2012

In this study, we are aimed to prevent grain growth of semi-solid AZ31 magnesium alloys during reheating process. The semi-solid AZ31+(Ca) billets were investigated by using metallographic analysis, X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy in order to elucidate the effect of Ca addition during reheating process. The grain growth of semi-solid AZ31+(Ca) billet was reduced with increasing Ca content during reheating. The grain size of AZ31+(Ca) billet decreased with increasing volume fraction of Al2Ca particles. The grain growth rate constant K calculated by Oswald ripening LSW theory in AZ31+1.5wt.% Ca billet was the lowest 129.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.281-284
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• 2007

The effect of Ca addition on the microstructure evolution and deformation behavior of AZ31 magnesium alloy produced by hot extrusion was investigated. For this purpose, Ca was added into AZ31 melts to the level of 0.7 and 2.0 wt.% Ca. Then, AZ31 base alloy and Ca modified AZ31 alloys were extruded at $383^{\circ}C$. Ca added alloys showed finer grain size and increased hardness value rather than AZ31 base alloy. After isothermal hot compression, the shape of tested specimen exhibited a noticeable anisotropy due to the crystallographic texture effect. The ratio of major and minor axes of ovality was not directly related to test condition and Ca amount. Flow stress level increases with the increase of Ca addition at temperature below $300^{\circ}C$ because of fine microstructure. However, at high temperature and low strain rate region ($400^{\circ}C$ and $10^{-3}s^{-1}$), reverse tendency was observed since main deformation mechanism changes from dislocation slip to grain boundary sliding or diffusional process at high temperature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.9
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• pp.997-1002
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• 2012

With the increasing demand for lightweight materials to reduce fuel consumption, especially in the transportation industry, magnesium alloys are being widely studied. However, there are several limitations to the large-scale application of magnesium alloys in a structure because of their low formability and strong anisotropy. In order to take into account both the strong anisotropy and tension-compression asymmetry of AZ31 sheet alloy, the Cazacu-Plunkett-Barlat yield criterion (Cazacu, 2006) was adopted in material modeling. The variation of the anisotropic coefficients that describe the yield surface evolution of AZ31 is optimized using an interpolation function based on specific calibration results. It generates continuous yield surfaces, which makes it possible to describe different hardening rates in tension and compression as well as the tension-compression asymmetry of magnesium alloys. The performance of the CPB06 yield criterion for simulating an axial crushing test was tested and compared with that of the Hill (1948) yield criterion.

• Proceedings of the KWS Conference
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• 2007.11a
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• pp.322-324
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• 2007

Nd:YAG laser welding of AZ31B-H24 magnesium alloy was carried out using AZ61 filler wire(Mg-6wt%Al-1wt%Zn). Microstructure and mechanical properties of welded joint were examined by optical microscopy, scanning electronic microscopy(SEM), energy dispersive spectroscopy(EDS), electron probe micro analyzer(EPMA) and victors hardness, tensile test at the room and elevated temperature. Test results indicate that the specimens welded with AZ61 filler wire have better tensile strength, elongation and victors hardness at room temperature than those of welded without filler wire. However tensile strength are similar but elongation are quite different at elevated temperature.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.311-312
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• 2012

PEO(Plasma Electrolytic Oxidation) 방법으로 인한 마그네슘 합금의 산화막 코팅시 Sodium Aluminate의 역할을 알아보았다. 전해액 내에 Sodium Aluminate 의 농도가 증가할수록 Plasma arc 발생에 필요한 전압의 상승이 빨라졌으며 그 산화막이 치밀해짐을 알 수 있었다. 또한 치밀한 산화막의 기공률은 분석하여 이를 내식성 결과와 비교함으로써 산화막의 기공률이 내식성에 미치는 영향을 고찰해보았다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.44-44
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• 2014

Magnesium alloy AZ31 sheet를 자동차용 부품으로 사용하기 위해서는 내식성, 전착도장성등의 신뢰성을 확보해야 한다. 이를 위해서 우리는 Phosphate, manganese, silicon계열의 화성처리제를 이용하여 자동차 부품으로 사용가능한 신뢰성확보를 위해 표면처리 방법에 관한 연구를 진행 하였다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.9-10
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• 2011

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.66.1-66.1
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• 2018

최근 자동차 배기가스 규제 및 전기자동차, 무인항공기 개발 등의 경량 소재에 대한 필요성이 지속적으로 증가하고 있다. 마그네슘 및 마그네슘 합금은 구조용 금속 소재 중 가장 밀도가 낮은 금속으로서 자동차, 항공, 기계 부품류 및 주방용품이나 전자제품 케이스류 등 다양한 산업분야에서 활용성이 크게 증가하고 있다. 하지만 마그네슘 합금은 화학적 반응성이 매우 크고 표면에 존재하는 피막의 치밀성과 화학적 안정성이 낮아서 쉽게 부식되는 단점이 있다. 따라서 내식성 향상을 위한 표면처리 기술 개발에 대한 필요성이 증대되고 있다. 양극 산화법은 금속표면에 양극 전류를 인가하여 산화피막을 인위적으로 형성시켜줌으로써 내식성을 향상시켜 주는 방법으로서 산업적으로 널리 사용되고 있는 표면처리 방법 중의 하나이다. 본 연구에서는 주석산나트륨의 농도에 따른 AZ31 마그네슘 합금의 양극 산화 피막 형성 거동을 연구하였다. DC 전류를 인가하여 양극산화 피막을 형성하였으며, 피막형성 전압 및 형성된 피막의 두께, 표면 거칠기 및 피막의 구조 등을 분석하여 주석산나트륨 농도에 따른 양극산화 피막의 형성 특성에 대하여 자세하게 고찰하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.2
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• pp.646-652
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• 2014

It is the primary aim of this paper to propose the empirical fatigue crack propagation model fit to describe a crack growth behavior of AZ31 magnesium alloys under the different specimen thickness conditions. The empirical models estimated are Paris-Erdogan model, Walker model, Forman model, and modified-Forman model. The parameters of each model are estimated by maximum likelihood method. The statistical crack growth data needed for an estimation of empirical models are obtained by fatigue crack propagation tests under the three cases of specimen thickness. It is found that the good empirical models fit to describe a crack growth behavior of AZ31 magnesium alloys under the different specimen thickness conditions are Paris-Erdogan model and Walker model. It is also verified that a fatigue crack growth rate exponent of a empirical model may be a material constant at the specimen thickness conditions of 4.75mm and 6.60mm.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.114-117
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• 2007

In the present study, the effects of initial texture on the twinning formation of AZ31 Mg rolled sheet was investigated. Uniaxial compression tests were performed on samples cut along the normal direction and rolling direction of rolled AZ31 Mg alloy sheet at various temperatures (RT, 200, 250, 300, 350, $400^{\circ}C$) with the 0.01/s strain rate. Pole figure of rolling planes showed that basal planes of most gain were located parallel to the rolling direction. After compression test, microstructures and stress-strain curves results indicated that active deformation twining occurred only at the specimen cut along the rolling direction. The slip-twin transition with the increase of temperature was also investigated.