| Along with the improvement of modern transport equipment to energy-saving, emission reduction and environmental protection requirements, magnesium alloy has been widely used in transportation and 3C fields because of the advantage of its lightweight, high strength, high damping, widely resource and easy recovery. It has showed a strong trend toward’on behalf of steel to Mg, on behalf of Al to Mg’. Magnesium alloy has become a hot research and exploitation of materials field at home and abroad. As a large nation of magnesium resources, we should seize the strategic opportunities to translate the resource advantages into industry advantages.In this paper, MB350 and KBM10, the two newly-developed AZ magnesium alloy, as research objects, OM, SEM, XRD and mechanic property tests were employed to explore their mechanic properties at room and elevated temperature and microstructure evolution. Also, the stress-strain curve of compression deformation of as-cast KBM10 was contained by means of high temperature compression. After Deform-3D numerical analysis simulating the metal forging process, Multiple forging experiment and transition coupler of super-plastic die forging forming experiment of the large size KBM10 were finished on the presser machine. Lastly, the new coupler were carried on the simple mechanics performance test. The research results are as follows:The grains of as-cast MB350 are coarse with the average grain size of 350μm, and the second phase widely distribute in the grain boundaries and inside the grains. The mechanical properties of as-cast MB350 is poor at room temperature, and its tensile strength and elongation are only 165MPa and 7.5%, respectively. After squeezing the grains are refined to 15μm. Besides, the strength and plasticity have been improved after extrusion, and the tensile strength and elongation of as-extruded MB350 are 296MPa and 20.1%, respectively. The optimum parameters of this experiment are that as-cast alloy is aged in 170℃ with 28 hours after it is dissolved in 440℃ with 4 hours and as-extruded alloy is aged in 170℃ with 24 hours directly.The mechanical properties of MB350 magnesium alloy has been studied at the temperature of 350℃-450℃ and the strain rate ranges of 10-4S-1-10-2s-1. The yield stress and flow stress of alloy decrease significantly and its plasticity increases simultaneously under the condition of high temperature tensile. At the beginning of the deformation, the flow stress increases to a maximum rapidly and then begin to decline after reaching peak stress, and gradually into the steady flow state, which is a characteristic of DRX in hot working. The flow stress increases with the increases of the stain rate at the same temperature, and decreases with the increase of the temperature when the strain rate keeps constant. The constitutive equation which is based on the hyperbolic sine model has been established by using the data of the elevated temperature tensile test of as-extruded MB350 and its average error is 4.86%. The stress exponent and the activation energy of the as-extruded alloy are 3.286 and 238kJ/mol, respectively.The compression rheological curve of as-cast KBM10 shows that it is positive strain rate sensitive material, that is the flow stress reduces with the temperature increases and the strain rate reduces. Using Deform-3D software, KBM10 magnesium alloy is stimulated. By four pass simulation compress, material shape of the original cylinder turns into a rectangle, and the size is also suit for coupling die forging.Combined with the existing experimental conditions, the multidirectional forging process is optimized to get the new forging coupler with excellent properties, the tension strength of which reaches 255MPa, the yield strength of which is 130MPa, and the extend rate is 6%. Hot-working safety process parameter is applied to the trial magnesium alloy coupling, and successfully produce some magnesium alloy transition coupler test products. |
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