| Magnesium alloys are widely used in automotive,electric and aeronautical industries due to their low density,good electromagnetic shielding characteristics, high damping characteristics,excellent machinability and so on.However,the application of magnesium alloys is far less than that of other metal materials because of its inherent properties,as lower strength,poor corrosion resistance and high-temperature performance and so on.Therefore,it is important to explore active approach of improving the mechanical properties and formability,in order to push the application of magnesium alloys and develop theirs performance advantages. Semisolid metal forming(SSM or SSF)can be widely used in many industries, meanwhile it belongs to net shape forming and advanced materials manufacturing technique as the formed parts possess more compact microstmcture,less entrapment of gas and better mechanical properties.So,Magnesium alloys are one of the most suitable materials for the semi-solid forming.The quality of semi-solid slurry has correlation with the parameter of the electromagnetic stirring in electromagnetic stirring.The purpose of this article is that the kinetic velocity and rule of the fluid during the process of electromagnetic stirring of semi-solid slurry of aluminum alloy will be found through the simulation of flow field with computer,and then the processing parameters of electromagnetic stirring will be optimized with the result of simulation.Firstly,the modeling and simulation of the coupling of the electromagnetic field and the flow field of electromagnetic stirring were done with the software ANSYS. And then the distribution of the magnetic lines of flux,the magnetic flux density of the magnetic field,the value of Lorentz force of the Magnesium alloy melt were obtained through the numerical simulation of the electromagnetic field.We can find two equal swirls distributed in the melting area lengthways from the result of the simulation of the flow field,the result accorded with the principle of the electromagnetic stirring.The maximal flowing velocity of the inner melt presents at the top right comer and the bottom right comer of the melting area.The minimal flowing velocity of the inner melt presents to the central area of the swirls.The elementary alteration rule of fluid field is been analyzed with the alteration of stirring frequency,current density,stirring temperature and ratio of height and diameter of Magnesium melt. The program of the experiment has been drawn up according to simulation parameter.Observing and comparing the microstructure of the test samples which were got from different stirring power(0.94 KW/kg,0.65 KW/kg,0.38 KW/kg) under different temperature(590℃,580℃,570℃),We can find the microstructures of test samples are optimal under the same stirring power when the temperature is 580℃.Therefore 595℃is a suitable temperature at stopping the electromagnetic stirring. Observing and comparing the microstructure of the test samples which were got from the same temperature(580℃) under different stirring power(0.94 KW/kg,0.65 KW/kg,0.38 KW/kg),We can find all of the primaryα-Mg grains are not fir-tree crystal but near-spherical and rose-shaped.The primaryα-Mg grains are the best-distributed,the smallest and roundest when the stirring power is 0.94 KW/kg. Therefore 0.94 KW/kg is a suitable stirring power for electromagnetic stirring.The theoretical analysis indicates that the strong flow motion leads to more even temperature field and solute field and stronger man-made temperature fluctuation in the AZ91D alloy melt so that the fine spherical primary grains are formed in the semi-solid AZ91D.In conclusion,the numerical simulation on the flow field of electromagnetic stirring of semi-solid slurry of magnesium alloy is a meaning of positive guidance to the experimental research to a certain degree. |
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