| Magnesium is known as the most potential"green metal"for development and application in the 21st century. With a series of advantages, such as specific strength and stiffness, light density, good thermal fatigue resistance, thermal conductivity, good vibration damping and electromagnetic shielding ability, rich resource, easy aging, easy recovery and so on, it is one of the most important lightweight and high-strength materials of this century. China's current production of magnesium and magnesium alloys is around 60-70 million tons, compared with more than 4,000 tons of production of aluminum and aluminum alloys, magnesium and magnesium alloy production is clearly too small, and its applications are far less than other mainly metals. This situation is mainly due to the low strength, brittleness, poor performance in corrosion resistance and high temperature of magnesium alloy material. To improve this situation, we need have a systematic and comprehensive study of magnesium alloys as a foundation. Herein, we studied the effect of three-dimensional rotating magnetic field and alternating traveling magnetic stirring on the solidification process of magnesium alloy and influence of magnesium alloy spiral magnetic stirring in the solidification process of magnesium alloy. Optical microscope (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), universal testing machine, TH160 Leeb Hardness and temperature acquisition system and other analysis and testing methods are employed to explore the changes of magnesium alloy solidification mechanism and conditions in three-dimensional magnetic field, thus getting solid foundation for the development of efficient and environment-friendly technology of magnesium alloy solidification.The results of imposing solidification process of magnesium alloy to three-dimensional magnetic field: (1) the morphology of primaryα-Mg phase changes from the traditional large-cast dendrites into petal-like shape and clumps. (2) the smallest average diameter ofα-Mg phase decreased by 19.0%, the largest average diameter ofα-Mg phase decreased by 43.9%, while the smallest form factor increased by 7.2%, the biggest form factor increase by 87.4%. (3) to increase the rotating magnetic field excitation voltage and reduce the mixing time are conducive to reducing the average grain diameter and shape factor increases, while the mixing time traveling magnetic field changes in the average grain diameter and shape factor are not significant . (4) the optimal process parameters: excitation voltage of 50V, 5s, and stirring time rotating magnetic field traveling wave magnetic stirring time 4s.Solidification process of magnesium alloy imposed spiral magnetic field results: (1) the morphology of primaryαphase a long dendrite arm into a rose-like dendrites and fine equiaxed grain. (2) The second-phaseβ-Mg17Al12 interrupted by the network, diffuse distribution of bone-shaped into a continuous distribution network in the grain boundary, and the increase in the number of second phase. (3)α-Mg phase of the X-ray diffraction peak of 2θangle with the small offset, that Al in solid solutionα-Mg phase the decrease of element content with the point of measurement results. (4) increase the maximum hardness of 38.5%, the maximum tensile strength increased 35.1% to 32.2% increase in the maximum elongation. (5) casting core temperature, and casting wall temperature difference between the non-magnetic stirring by the time of 6-10℃reduced to 1-3℃. (6) mold wall measured eutectic temperature without magnetic field by the time of stirring increased to 409℃425℃, mold center measured eutectic temperature without magnetic stirring by the time of 413℃to 426℃. (7) Al in the matrixαphase without magnetic field by the mixing ratio of 8.36% when reduced to 5.62%,βphase in the second phase without magnetic stirring by the time of 30.07% to 41.96%, in a total ofα+βno significant changes in crystal phase.Theoretical analysis: (1) spiral magnetic stirring to change the flow of liquid magnesium alloy state, so that when the magnesium alloy solidification temperature of liquid consistency. (2) spiral magnetic field, the clusters move from the liquid to the solid phase than that required to overcome the barrier when no magnetic field reduction, help to improve the nucleation rate of primaryαdwarf, so the purpose of grain refinement. (3)α-phase content of the aluminum element is relatively low, it is not easy to crystallize dispersedβphase, on the contrary, the final solidification of liquid aluminum content is high, it is easy to mold a continuous distribution ofβphase.
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