세계적인 환경 규제로 인해 마그네슘 합금과 같은 경량 소재에 대한 수요가 증가하고 있으며, 마그네슘 합금 소재의 다양한 산업계 적용을 위한 용접 및 접합 방식에 대한 연구도 지속적으로 수행되고 있다. 앞선 Part I 연구에서는 마그네슘 합금에 대한 파이버 레이저 Bead on Plate(BOP) 실험을 수행하여 맞대기 용접 조건의 확보를 위한 기초 연구를 수행하였으며, 본 연구에서는 Part I의 기초 BOP 실험에서 도출된 적합한 레이저 출력과 용접 속도를 바탕으로 두께 3mm의 AZ31B 마그네슘 합금에 대해 맞대기 용접을 시행하였고, 인장시험 및 경도시험을 수행한 후 기계 물성 데이터를 분석하였다. 분석 결과 레이저 출력 2.0 kW, 50 mm/s (Heat input)의 조건에서 항복강도 151.5 MPa, 인장강도 224.1 Mpa으로 우수한 인장, 항복강도를 얻을 수 있었다.

Research into lightweighting to improve vehicle fuel efficiency and reduce exhaust emissions continues as environmental regulations become increasingly stringent. Magnesium alloys, chosen for their lightweight properties, are more than 35% lighter than aluminum alloys and also exhibit excellent mechanical characteristics. While magnesium alloys are commonly utilized in arc welding processes like GTAW and GMAW, they pose challenges such as high residual stresses and welding defects. Laser welding, on the other hand, offers the advantage of precise heat input, enabling deep and high-quality welds while minimizing welding distortion. In this study, fiber laser welding was employed to weld a 4.0mm thick AZ31B-H24 using the Bead on Plate technique. A total of 10 different welding conditions were tested with fiber laser welding, and the cross-sections of the weld beads were examined. Weld bead shapes were measured based on five parameters. The results allowed for an evaluation of the weldability of AZ31B-H24 using fiber laser welding.

The purpose of this research is to investigate the statistical behavior of fatigue crack propagation(FCP) in magnesium alloy AZ31. FCP tests have been performed on compact specimens of AZ31 at load ratio conditions and maximum fatigue load conditions to obtain statistical data of FCP. It was found that the variability of fatigue crack propagation rate was significantly large at initial stage of FCP and gradually became smaller as the fatigue crack propagated. The finding of the study showed that increasing the load ratio could increase the variability of fatigue crack propagation rate at initial FCP stage. The samller the load ratio, the higher the fatigue crack propagation rate at initial stage. It was also found that the load ratio is a factor affecting the fatigue crack propagation rate in magnesium alloy.

Magnesium alloy is the lightest practical metal. It has excellent specific strength and recyclability as well as abundant reserves, and is expected to be a next-generation structural metal material following aluminum alloy. This paper investigated the possibility of thin plate fabrication by applying a overheating treatment to the melt drag method, and investigating the surface shape of the thin plate, grain size, grain size distribution, and Vickers hardness. When the overheating treatment was applied to magnesium alloy, the grains were refined, so it is expected that further refinement of grains can be realized if the overheating treatment is applied to the melt drag method. By applying overheating treatment, it was possible to fabricate a thin plate of magnesium alloy using the melt drag method, and a microstructure with a minimum grain size of around 12 μm was obtained. As the overheating treatment temperature increased, void defects increased on the roll surface of the thin plate, and holding time had no effect on the surface shape of the thin plate. The fabricated thin plate showed uniform grain size distribution. When the holding times were 0 and 30 min, the grain size was refined, and the effect of the holding time became smaller as the overheating treatment temperature increased. As the overheating temperature becomes higher, the grain size becomes finer, and the finer the grain size is, the higher the Vickers hardness.

Research is being actively conducted on the continuous thin plate casting method, which is used to manufacture magnesium alloy plate for plastic processing. This study applied a heat transfer solidification analysis method to the melt drag process. The heat transfer coefficient between the molten magnesium alloy metal and the roll in the thin plate manufacturing process using the melt drag method has not been clearly established until now, and the results were used to determine the temperature change. The estimated heat transfer coefficient for a roll speed of 30 m/min was 1.33 × 105 W/m2·K, which was very large compared to the heat transfer coefficient used in the solidification analysis of general aluminum castings. The heat transfer coefficient between the molten metal and the roll estimated in the range of the roll speed of 5 to 90 m/min was 1.42 × 105 to 8.95 × 104 W/m2·K. The cooling rate was calculated using a method based on the results of deriving the temperature change of the molten metal and the roll, using the estimated heat transfer coefficient. The DAS was estimated from the relationship between the cooling rate and DAS, and compared with the experimental value. When the magnesium alloy is manufactured by the melt drag method, the cooling rate of the thin plate is in the range of about 1.4 × 103 to 1.0 × 104 K/s.

생체용 마그네슘 합금은 전연성 부족과 열에 의한 팽창률 변화가 심하여 2mm 이하의 판재를 만드는 것이 매우 어려움 문제이다. 이를 해결하기 위해 압연 방식, 세이퍼 방식, 밀링 방식 등의 다양한 방법이 존재할 수 있다. 압연 방식을 적용하여 실험을 진행하였으나 Mg 합금은 전연성, 취성의 문제로 인해 파괴되는 현상이 발생하였다. 그리고 세이퍼 방식은 가공시 충격이 발생하는 단속절삭이기 때문에 표면에 자국이 남게 되고 시험편이 휘어지는 현상이 발생하는 문제가 발생하였다. 최종적으로 밀링 방식으로 전환하여 가공실험을 수행해 본 결과 매우 만족할 만한 결과값을 얻게 되었고, 이 결과는 절삭조건을 절삭회전수 1000rpm, 이송속도 127mm/rev, 절삭깊이 0.5mm로 엔드밀 사용하여 가공하였을 때 Ra = 0.44㎛의 표면거칠기값을 얻게 되었다. 본 논문에서는 생체 마그네슘 합금재료로 미소판재를 가공하였을 때 매우 좋은 표면을 유지하며 2mm 이하의 미소 두께를 지속적으로 가공이 가능하도록 하였으며, 다양한 절삭조건, 2날과 4날 엔드밀 날수 변화 등을 통해 최적의 가공조건을 알아보는 실험을 진행하였다.

AZ31 magnesium alloy was used to manufacture a thin plate using a melt drag method. The effects of roll speed, molten metal temperature, and molten metal height, which are the basic factors of the melt drag method, on the surface shape, the thickness of the thin plate, Vickers hardness, and microstructure of the thin plate were investigated. It was possible to manufacture AZ31 magnesium alloy thin plate at the roll speed range of 1 to 90 m/min. The thickness of the thin plate, manufactured while changing only the roll speed, was about 1.8 to 8.8 mm. The shape of the solidified roll surface was affected by two conditions, the roll speed and the molten metal height, and the Vickers hardness of the manufactured magnesium alloy thin plate value ranged from Hv38~Hv60. The microstructure of the thin plate produced by this process was an equiaxed crystal and showed a uniform grain size distribution. The grain size was greatly affected by the contact state between the molten metal and the solidification roll, and the amount of reactive solids and liquids scraped at the same time as the thin plate. The average grain size of the thin plate fabricated in the range of these experimental conditions changed to about 50-300 μm.

The objectives of this paper are to evaluate the factors affecting the fatigue crack propagation(FCP) behavior in AZ31 magnesium alloy. FCP experiments have been performed on the specimens of AZ31 magnesium alloy under various conditions such as a loading frequency, a specimen thickness, a maximum fatigue load, and a load ratio and the obtained results were analyzed to find the influence factors on the FCP behavior in magnesium alloy. It is necessary to consider the influence factors for the design and the maintenance of lightweight structures. The correlation between the crack growth rate exponent and the crack growth rate coefficient, which are FCP behavior parameters, was also analyzed and the regression model was presented.

To improve the shortcomings and expand the advantages of the single-roll melt drag method, which is a type of continuous strip casting method, the melt drag method with a molding belt is applied to AZ31 magnesium alloy. By attaching the forming belt to the melt drag method, the cooling condition of the thin plate is improved, making it possible to manufacture thin plates even at high roll speed of 100 m/min or more. In addition, it is very effective for continuous production of thin plates to suppress oxidation of the molten metal on the roll contact surface by selecting the protective gas. As a result of investigating the relationship between the contact time between the molten metal and the roll and the thickness of the sheet, it is possible to estimate the thickness of the sheet from the experimental conditions. The relationship between the thin plate thickness and the grain size is one in which the thinner the thin plate is, the faster the cooling rate of the thin plate is, resulting in finer grain size. The contact state between the molten metal and the roll greatly affects the grain size, and the minimum average grain size is 72 μm. The thin plate produced using this experimental equipment can be rolled, and the rolled sample has no large cracks. The tensile test results show a tensile strength of 303 MPa.

An investigation is performed to clarify the manufacturing conditions of pure magnesium and AZ31 magnesium alloy thin plate using the melt drag method. By the melt drag method, suitable for magnesium molten metal, pure magnesium can be produced as a continuous thin plate with a thickness of 1.4 mm to 2.4 mm in the range of 5 m/min to 20 m/min of roll speed, and the width of the thin plate to the nozzle outlet width. AZ31 magnesium alloy is able to produce a continuous sheet of thickness in the range of 5 m/min to 30 m/min in roll circumferential speed, with a thickness of 0.6 mm to 1.6 mm and a width of the sheet matching the nozzle outlet width. In the magnesium melt drag method, the faster the circumferential speed of the roll, the shorter the contact time between the molten metal and the roll, and it is found that the thickness of the produced thin plate becomes thinner. The effect of the circumferential roll speed on the thickness of the thin plate is evident in the low roll circumferential region, where the circumferential speed is 30 m/min or less. The AZ31 thin plate manufactured by the melt drag method has a finer grain size as the thickness of the thin plate decreases, but it is currently judged that this is not the effect of cooling by the roll.

Recently magnesium alloy sheet has been used as a lightweight material in transportation area. Warm forming is a forming method that improves formability and reduces springback. The magnesium alloy sheet has a characteristic that large difference of flow stress increases depending on strain rate at high temperature. These characteristics cause low dimensional accuracy of formed products. In this study, experiments were performed on the 2D-draw bending with respect to the temperature and forming speed in order to investigate the effects of strain rate and temperature. It was found that as the temperature increases, spinrgback of 2D-draw bending decreased and formability of AZ31B increased. Additionally, the effect of the punch speed was investigated. At 250°C, as the punch speed increased, the springback of 2D-draw bending decreased.

In this study, the mechanical characteristics with micro structure were analyzed on the butt joint of AZ60 magnesium material extruded by GMAW and GTAW processes. As the result of tensile test, the fracture in the welding joint area happened at both processes and seemed to be brittle fracture. The yield strength of GMAW was 84.29% and GTAW was 60.43% as compared with base metal. The yield strength of GMAW was higher 23.86% than that of GTAW. The result of decreased micro hardness was indicated at both processes. The value of minimum micro hardness in FZ at GMAW was Hv 46.7 and GTAW was Hv 43.6 as compared with base metal. The value of minimum micro hardness at GMAW process was higher 5.64 % than that at GTAW process. The size of grain boundary at GMAW process in HAZ is smaller than that at GTAW process. GMAW process is more superior than GTAW process from the productivity and quality in case of automatic welding for magnesium alloy such as the automobile seat frame.

Magnesium alloys are of emerging interest in the automotive, aerospace and electronic industries due to their light weight, high specific strength, damping capacity, etc. However, practical applications are limited because magnesium alloys have poor formability at room temperature due to the lack of slip systems and the formation of basal texture, both of which characteristics are attributed to the hcp crystal structure. Fortunately, many magnesium alloys, even commercialized AZ or ZK series alloys, exhibit superplastic behavior and show very large tensile ductility, which means that these materials have potential application to superplastic forming (SPF) of magnesium alloy sheets. The SPF technique offers many advantages such as near net shaping, design flexibility, simple process and low die cost. Superplasticity occurs in materials having very small grain sizes of less than 10 μm and these small grains in magnesium alloys can be achieved by thermomechanical treatment in conventional rolling or extrusion processes. Moreover, some coarse-grained magnesium alloys are reported to have superplasticity when grain refinement occurs through recrystallization during deformation in the initial stage. This report reviews the characteristics of superplastic magnesium alloys with high-strain rate and coarse grains. Finally, some examples of SPF application are suggested.

The effect of adding Ca on the microstructural and mechanical properties of as-cast Mg-11Li-3Zn-1Sn(wt%) alloys were investigated. Mg-11Li-3Zn-1Sn-0.4Mn with different Ca additions (0.4, 0.8, 1.2 wt%) were cast under an SF6 and Co2 atmosphere at 720 oC. The cast billets were homogenized at 400 oC for 12h and extruded at 200 oC. The microstructural and mechanical properties were analyzed by OM, XRD, SEM, and tensile tests. The addition of Ca to the Mg-11Li-3Zn-1Sn-0.4Mn alloy resulted in the formation of Ca2Mg6Zn3, MgSnCa intermetallic compound. By increasing Ca addition, the volume fraction and size of Ca2Mg6Zn3 with needle shape were increased. This Ca2Mg6Zn3 intermetallic compound was elongated to the extrusion direction and refined to fine particles due to severe deformation during hot extrusion. The elongation of the 0.8 wt% Ca containing alloy improved remarkably without reduction strength due to the formation of fine grain and Ca2Mg6Zn3 intermetallic compounds by Ca addition. It is probable that fine and homogeneous Ca2Mg6Zn3 intermetallic compounds played a significant role in the increase of mechanical properties.

마그네슘은 일반적인 금속 중 가장 큰 화학적 활성을 가지므로, 이에 따라 마그네슘 합금도 내식성을 갖기위한 전처리가 필요하다. 본 연구는 여러 가지 유기산으로 전처리하여 양극 산화된 마그네슘 합금의내식성에 대하여 조사하였다. 유기산은 옥살산(Oxalicacid), 구연산(Citricacid), 초산(Aceticacid)을 사용하였다. 생성된 피막의 표면에 대한 morphology와 조성 그리고 전기화학적 물성을 평가하는 실험을진행하였다. 양극 산화된 표면의 morphology는 SEM을 통해 관찰하였고, EDS 분석 결과 산화 피막은Mg, O, Al로 이루어져 있음을 확인하였다. 산화 피막의 내식성을 조사하기 위해 3.5 wt.% NaCl 용액에서 동전위 분극시험(potentiodynamicpolarizationtest)과 electrochemical impedance spectroscopy(EIS)를 분석하여 AZ91D Mg alloy의 내식성을 알 수 있었다. 이 결과에서 구연산과 초산으로 전처리한양극 산화 피막이 내식성을 향상시켰음을 알 수 있었다.

Recently, consumption of magnesium alloys has increased especially in the 3C (computer, communication, camera) and automobile industries. The structural application of magnesium alloys has many advantages due to their low densities, high specific strength, excellent damping and anti-eletromagnetic properties, and easy recycling. However, practical application of these alloys has been limited to narrow uses of mild condition, because they are inferior in corrosion resistance and wear resistance due to their high chemical reactivity and low hardness. Various wet and dry processes are being used or are under development to enhance alloy surface properties. Various conversion coating and anodizing methods have been developed in a view of eco-friendly concept. The conventional technologies, such as diffusion coating, sol-gel coating, hydrothermal treatment, and organic coating, are expected to be newly applicable to magnesium alloys. Surface treatments for metallic luster or coloring are suggested using the control of the micro roughness. This report reviews the recent R&D trends and achievements in surface treatment technologies for magnesium alloys.

Zr-Ti alloy powders were successfully synthesized by magnesium thermal reduction of metal chlorides. The evaporated and mixed gasses of were injected to liquid magnesium and the chloride components were reduced by magnesium leading to the formation of . The released Zr and Ti atoms were then condensed to particle forms inside the mixture of liquid magnesium and magnesium chloride, which could be dissolved fully in post process by 1~5% HCl solution at room temperature. By the fraction-control of individually injected and gasses, the final compositions of produced alloy powders were changed in the ranges of Zr-0 wt.%~20 wt.%Ti and their purity and particle size were about 99.4% and the level of several micrometers, respectively.