Magnesium - Science, Technology and Applications

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Authors: Yu Yoshida, Keita Arai, Shigeharu Kamado, Yo Kojima
Abstract: Ingots of AZ31 alloys were prepared for the present study. The ingots were hot rolled to 0.5 mm thickness. In order to develop rolled magnesium alloy sheet having excellent plastic formability, the authors attempted the grain refinement and randomization of the rolling texture of the alloy by means of surface modification utilizing wet-type shot blast (wet blast) and subsequent annealing. Then the microstructural observations including texture analysis and tensile tests were carried out. Furthermore, the bendability and stretch formability were investigated. After wet blast and subsequent annealing at 573K for 1h, the region of 50 µm depth from the sheet surface that experienced deformation by wet blast is recrystallized, and fine and equiaxed grains are generated. Although rolling texture remained in the central part of the sheet, the recrystallized grains near the surface of such specimens have random crystallographic orientation. The tensile strengths of both rolled and wet-blasted specimens are almost the same but the elongation of the latter increases due to grain refinement and randomization of crystallographic orientation. Such a microstructural feature realizes bending with the radius of 1 mm without cracks and wrinkles and leads to an increase in limiting stretching depth by 1.5~2 mm.
449
Authors: Shi Hong Zhang, Yong Chao Xu, G. Palumbo, S. Pinto, Luigi Tricarico, Z.T. Wang, Q.L. Zhang
Abstract: Comparing the formability with each other, extrusion and various rolling experiments were carried out to make fine-grained AZ31 Mg sheets, and uni-axial tensile tests were carried out at different strain rates and temperatures to investigate the effect of different variables. A warm deep drawing tool setup with heating elements, which were distributed under the die surface and inside the blank holder, was designed and manufactured, and deep drawing was performed. Extruded Mg alloy AZ31 sheets exhibit the best deep drawing ability when working in the temperature range 250-350°C. Extruded and rolled sheets of 0.8 mm thick were also deep drawn in the lower temperature range 105-170°C,showing good formability and reaching a Limit Drawing Ratio up to 2.6 at 170°C for rolled sheets. At last, a sheet cup 0.4 mm thick was deep drawn successfully at 170 °C.
453
Authors: Jong Kwan Hwang, Keun Yong Sohn, Dae Min Kang, Young Su Shin
Abstract: In this paper, the distribution of temperatures on specimen and the variations in punch forces on friction coefficients during press forging of AZ31 sheets have been analyzed by Finite Element Analysis technique. Results show that the top of rib and boss areas showed lower temperatures than other areas because of the heat dissipation to air by radiation. The foot regions of the rib and boss showed greater temperature rise due to greater plastic flow. The applied punch force significantly increased at 473K or lower temperatures indicating the forming temperature of AZ31 sheet should not lower than 473K. The friction condition of the punch influenced more significantly on the materials flow pattern compared to those of the die. Using a lubricant on the contact area between the punch and specimen would effectively reduce the punch force and enhance the forming capability.
457
Authors: Yong Chao Xu, Shi Hong Zhang, H.M. Liu, Z.T. Wang, W.T. Zheng, Q.L. Zhang, Y. Xu
Abstract: The extruded sheets were prepared at the temperature between 350ıand 400ı, and the magnesium alloy sheet was manufactured by a new method, cross rolling, in which the rolling direction was changed in each pass. At the time, deep drawing of magnesium alloy sheet was investigated at elevated temperatures. The results show that the sheet has refined-grain by cross-rolling after it was annealed at 250ı, and the formability is significantly improved at lower temperatures, which is superior to the extruded sheet and the one-way rolled sheet. Deep drawing of magnesium alloy was performed successfully, and cylindrical cup of limited drawing ratio (LDR) 2.6 and 35 mm deep rectangular box (65ı50) was achieved at the lower temperature of 170ı. The different types of fracture were analyzed and reasonable parameters were determined.
461
Authors: Jian Yih Wang, Yung Hung Chen, Yi Lang Yang, Shyong Lee
Abstract: Among the conventional and alleged bulk deformation processes in metalworking, equal channel angular extrusion (ECAE) is an innovative and attractive method to refine grain structures effectively. Grain refining by this process on magnesium alloy AZ31 was studied and compared to published data. An interesting and unique question is proposed and studied - that is, how dominant is the accumulated strain as obtained through multiple angular extrusion passes. Tensile tests were performed at room and high temperatures, and processed AZ31 was examined with optical and transmission electron microscopy as well as x-ray diffraction.
465
Authors: Yuichi Miyahara, Kazuhiko Adachi, Yasuhiro Maehara, Z. Horita, Terence G. Langdon
Abstract: A commercial AZ31 Mg alloy was subjected to ECAP (equal-channel angular pressing) and the tensile properties were examined at room temperature. It is shown that the microstructure before ECAP significantly affects the performance of ECAP without breaking samples. When the initial structure before ECAP is homogeneous with equiaxed grains, subsequent ECAP is feasible at lower temperatures. The grain refinement is achieved more effectively as the temperature for ECAP is lowered and the number of ECAP pass is increased. The tensile ductility was reduced after 1 pass of ECAP at 473 K or 498 K. However, the ductility was improved with an increasing number of ECAP pass or by annealing at 473 K or 523 K after ECAP. The results demonstrate that a homogeneous distribution of fine equiaxed grains is important for ductility improvement in the AZ31 Mg alloy.
473
Authors: Alan A. Luo, Anil K. Sachdev
Abstract: An appropriate temperature (150-200°C) bending process has been developed for AZ31 and AM30 magnesium alloy tubes, and the optimum bending process parameters were obtained using a Design of Experiments (DOE) method. The development of this process was one of the key factors for use of magnesium tubes in automotive components for vehicle weight reduction. The tensile properties and deformation microstructure of magnesium alloys at elevated temperatures indicated that temperature of 150-200°C which might be suitable for hydroforming and other forming processes.
477
Authors: Ming Zhou, Jianyong Cao, Fulin Yu, Xia Wei
Abstract: Compared with any other pressure processing methods, extrusion is more prone to develop the plasticity of the metal. Extrusions have much better size precision and surface quality than products by rolling and forging. As one-shot molding process, extrusion can eliminate some machining. In addition, extrusions have very high strengths and elongations because of their compact interior structures and fine grains. This paper summarizes some experiences and plans in extrusion production of CQMST(Chongqing Magnesium Science & Technology Co.Ltd). Magnesium, a plentiful element with density of 1.78g/cm3,2/3 of aluminum and 1/4 of steel, is characterized by its high specific strength and toughness, good dumping performance, thermal conductivity and electromagnetism shielding as well as recyclability. Following the advancing technologies of magnesium smelting, high pressure processing, surface treatment and soldering since 1990’s, the prices of magnesium and its ingot stepped down. As an important light engineering material, magnesium application is growing at annual speed of 15%, much higher than aluminum, copper, zinc, nickel and steel. In China, magnesium and magnesium alloy development, application and industrialization has been placed on the National “Tenth Five-year Plans” and the National “863” Scheme, which indicated the coming of new age for magnesium and magnesium alloy development and application in China. In the past, most of the magnesium products were produced by casting, especially die casting and thixomolding. It’s always considered that the crystal structure of magnesium is hexagonal close-packed, and only two slip planes exist at room temperature, so compared with other alloys, it’s very difficult to produce magnesium parts by forging, rolling or extrusion. Nevertheless, practice showed that if heated to a certain temperature, magnesium extrusion may not be hard work, and even easier than 5056 and 2024 aluminum. When extruded with distributary die, magnesium alloy can have better soldering performance than aluminum alloys mentioned above, just because new slip system forms along with increasing temperature (>225°C) and accordingly increases the plasticity of magnesium.
483
Authors: Kanichi Hatsukano, Kunio Matsuzaki, Toru Shimizu, Kichitaro Shinozaki
Abstract: The Formability of magnesium wrought alloys, AZ61 and AZ31 were investigated . First, the cylinder compression tests were carried out at room temperature and elevated temperatures. Then, the possibility of applying the warm lateral extrusion of the AZ61 and AZ31 alloys were examined under several conditions by using the multi-axes material testing machine. A cylindrical billet coated with molybdenum disulfide lubricant was set in the horizontal die cavity and the billet was heated up to the extrusion temperature, and then extruded laterally under the two horizontally advancing punches. Furthermore, lateral extrusion with counteracting pressure on the end of branches by using two punches methods was tried to reduce the extrusion temperature and sound products was obtained around 190°C.
487
Authors: J. Swiostek, Jan Bohlen, Dietmar Letzig, Karl Ulrich Kainer
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