| Magnesium alloys are the lightest structural metallic materials in the earth and the researches and applications of magnesium alloys have attracted much attention recently,especially the development of wrought magnesium alloys is rapid.At present,to control the widely used Mg-Al series alloys refinement,homogenization and composition segregation is a hot topic.In this paper,AZ80 alloy with high Al content was selected as research object,and different electromagnetic fields were used to treat the melt.The flow behavior and temperature field of the melt under different magnetic fields were investigated by numerical simulation,and then the optimized parameters through the numerical simulation were applied to the melt treatment.,The variation of the solidification microstructures of the experimental AZ80 alloys under different magnetic fields were investigated,and it could provide theoretical and technical methods for the large size magnesium alloy ingot preparation.1 The heat convection of AZ80 alloy melt is insufficient to cause the strong flow of the melt without treated in mold,so the temperature distribution is extremely inhomogeneous during the solidification process.However,the AZ80 alloy is under repeatedly tension and compression with pulsed magnetic field,and the maximum electromagnetic pressure stress is much higher than the electromagnetic tensile stress.Different flow speeds in different regions of the melt are generated under the applied pulsed magnetic field,and then the strong shearing effect generated in the melt,so as to achieve more evenly distributed temperature field.is.2 Strong convection and agitation are generated in AZ80 alloy melt under both single pulse magnetic field and out-phase magnetic field,but the agitation regions and strength in melt generated by single pulse magnetic field and out-phase magnetic field are different.the AZ80 alloy melt has higher flow velocity and larger value of oscillation under the influence of outphase magnetic field,thus more homogeneously distributed temperature field could be reach in the out-phase magnetic field condition.It is beneficial to obtain homogeneous microstructure and simultaneous melt solidification.3 The extreme value of repeatedly tension and compression and the difference between tensile and compression increase with the increasing current intensity of out-phase magnetic field.Afterwards,the overall oscillation and the flowability of the melt enhance,so as to acquire evenly distributed temperature field.When the current frequency of out-phase magnetic field increases,the tensile and compression effected region decreases,the flowing difference of difference melt location becomes lager and the vibration velocity of melt decreases.The effect of the frequency variation on the temperature field is smaller than the variation of current intensity.The superior flowability and temperature field distribution of the AZ80 alloy melt could be achieved at the frequency of 30Hz and 150A current intensity.3 Out-phase magnetic field created by different coil series have different effects on flowability and temperature field of the melt.The Out-phase magnetic field created by alternating series generates lower lorentz force compared with the Out-phase magnetic field created by continuous series,but the repeatedly tension and compression time increases,the melt flow rate decreases and the temperature inhomogeneity increases slightly.The grain refinement effect under out-phase magnetic field created by continuous coil series and alternating coil series during AZ80 alloy solidification process is different.4 The effect of single pulsed magnetic field on the grain refinement of AZ80 alloy during the solidification process is obvious.The grain size of AZ80 alloy decreases with the increasing current and frequency.Grain refinement effect between the single pulse magnetic field and the out-phase pulsed magnetic field is different.Uniformly and finely distributed grains could be obtained under the lower current intensity of out-phase pulsed magnetic field compared with the single pulse magnetic field,but the frequency change has little effect on the grain refinement of AZ80 alloy.Compared with the absence of an applied magnetic field,the grain refinement effect of out-phase pulsed magnetic field on AZ80 alloy improves 60 to 80%,and the grain refinement degree improves about 20%to 50%compared with the single pulsed magnetic field. |
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