| The effects of the size and shape of the crucible on the quality of semisolid alloy slurry were studied in the semisolid slurry fabrication process.By changing the size and shape of the crucible can control the effective nucleation rate,increasing the uniformity of melt microstructure.What's more,the change of geometry can control the flow status,can promote two stream formation,and strengthen melt mixing and flow and heat transfer at internal,increase the uniformity of heat dissipation.Under the effect of constant electromagnetic frequency,the change of melt flow can be realized by changing the size of crucible,which is expected to influence the solidification microstructure of melt,and the process is simpler and more energy efficient.The proper radius of crucible,the shape of crucible and the parameters of electromagnetic stirring can be used to lay the foundation for exploring the new technology of high efficiency and economical control theory and technology and industrial production of high-performance semisolid aluminum alloy.In this work,the effects of the size and shape of the crucible on the liquid-solid phase transformation,electromagnetic field,flow rate and temperature distribution and solidification microstructure of semisolid A356 aluminum alloy were systematically studied by numerical simulation and experimental research.The effect of crucible radius on the liquid-solid phase transformation and the electromagnetic field of A356 aluminum alloy was investigated.With the increase of crucible radius,the longer the time required for the complete liquid-solid phase transition at the end point of the crucible.The magnetic flux density gradually increasing from the crucible center to the crucible at about 0.85 times the distance of the crucible radius,and the electromagnetic force gradually increasing from the crucible center to the crucible at about 0.9 times the distance of the crucible radius.The influences of crucible radius and the electromagnetic frequency on the maximum flow rate and temperature distribution of the semisolid A356 aluminum alloy were further studied.It is found that the maximum flow rate increasing with the increase of crucible radius and the electromagnetic frequency.When the electromagnetic frequency is 30 Hz and the crucible radius is 30 mm,the maximum flow rate is 148.9mm/s.When the crucible radius is constant,the temperature distribution becomes more and more uniform with the increase of the electromagnetic frequency.When the crucible radius is 30 mm,the high quality semisolid aluminum alloy slurry can be fabricated by the existing experimental equipment.Based on the research of the larger crucible radius,the design idea of the non-circular crucible was put forward.It is hoped that the alloy melt on the same horizontal surface in the crucible has different flow rates and flow state under the action of electromagnetic stirring.Therefore,the effect of the major and minor axial ratio of crucible on the liquid-solid phase transformation and the electromagnetic field of A356 aluminum alloy was studied.With the increase of the major and minor axial ratio of crucible,the time required for the complete liquid-solid phase transformation at the end point of the minor axis varies little,while the time required for the complete liquid-solid phase transformation at the end point of the major axis gradually decreases.When the major and minor axial ratio of crucible is from 1.1 to 1.3,the maximum electromagnetic force at about 0.9 times the distance on the major axis firstly decrease and then increase,the maximum electromagnetic force at about 0.9 times the distance on the minor axis gradually decreases.When the major and minor axial ratio of crucible is 1.1,the average value of the magnetic flux density is smaller,the distance of almost 0 of the magnetic flux density is moderate,and the average value of the electromagnetic force is maximum.The effects of the major and minor axial ratio of crucible and the electromagnetic frequency on the maximum flow rate and temperature distribution of the semisolid A356 aluminum alloy were further studied.The results show that the greater the major and minor axial ratio of crucible,the maximum flow rate of the semisolid A356 aluminum alloy at the minor axis firstly increase and then decrease,and the maximum flow rate of the semisolid A356 aluminum alloy at the major axis increase first,then decrease and then increase.The higher the electromagnetic frequency,the flow rate difference of the semisolid A356 aluminum alloy at the minor axis and the major axis are apparent,so that occurs the phenomenon of "acceleration-deceleration-acceleration" in the melt flow.When the electromagnetic frequency and the major and minor axial ratio of crucible are 30 Hz and 1.1 respectively,the maximum flow rate at the major axis and the minor axis of the crucible are 153.6 and 143.2mm/s respectively,and the flow rate difference is the smallest.When the major and minor axial ratio of crucible is constant,the temperature gradient decrease with the increase of the electromagnetic frequency,and the temperature distribution becomes more and more uniform.When the major and minor axial ratio of crucible is 1.1,the high quality semisolid aluminum alloy slurry can be fabricated by the existing experimental equipment.The effects of the major and minor axial ratio of crucible,the electromagnetic frequency and the stirring time on the microstructure of the semisolid A356 aluminum alloy slurry were investigated.When the major and minor axial ratio of crucible,the electromagnetic frequency and the stirring time are 1.1,30 Hz and 12 s respectively,better semisolid A356 aluminum alloy slurry can be fabricated at this condition. |
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