Effect Of Rotating Magnetic Field On Microstructure And Mechanical Properties Of Cast Magnesium Alloy

It is known that electromagnetic stirring can refine the grain and improve the mechanical properties of magnesium alloy.However,the microstructure and properties of magnesium alloy are different under the condition of applying different stirring parameters.In this paper,the Mg-Al-Zn-based alloy was used as the experimental material to study the effect of rotating magnetic field on the microstructure and mechanical properties of magnesium alloy tube under different stirring parameters(the stirring frequency and the magnetic field current were changed).Ansoft and Fluent software were used to simulate the electromagnetic field and temperature field of the magnesium alloy during the solidification process,and thus studied the influence of electromagnetic stirring parameters on magnetic field and temperature field.The results show that the distribution of the rotating magnetic field is the same in one cycle at different time,and the rotation period is the same as the current change period.As the magnetic field current increases,the maximum magnetic induction intensity and the maximum electromagnetic force increases gradually;when the stirring frequency increases,the maximum magnetic induction intensity decreases,while the maximum electromagnetic force of the melt gradually increases.Under different stirring parameters,the magnetic induction intensity along the radial direction decreases first and then increases,and the electromagnetic force increases gradually.Electromagnetic stirring can change the heat transfer condition of the molten metal,so that the temperature of the magnesium alloy solution solidification process tends to be uniform.When the stirring frequency is 6Hz,the magnetic field current is 90 A,120A,150 A corresponding to the undercooling of 2.5°C,4°C,4.5°C.The bigger the magnetic field current is,the faster the AZ31 magnesium alloy melt cools,and more helpful to increase the nucleation rate and gradually refine the grain.When the magnetic field current is 150 A,the stirring frequency is 6Hz,8Hz,10 Hz corresponding to the undercooling of 4°C,5°C,6.5°C,and the higher the stirring frequency is,the faster the AZ31 magnesium alloy melt cools,and more helpful to increase the nucleation rate and gradually refine the grain too.The larger the magnetic field current or the greater the stirring frequency,the better the grain refinement effect,When the magnetic field current is 150 A,a lot of twin crystal were produced in the grain of AZ31 magnesium alloy which can improve the tensile strength and yield strength of the alloy.The ?-Mg17Al12 phase gradually dissolved into the ?-Mg matrix and formed some tiny second-phases,Also increased the solid solubility of Al atoms in the matrix thus improve the elongation of the alloy.The larger the magnetic field current or the greater the stirring frequency,the better the mechanical properties of the magnesium alloy.When the magnetic field current is 150 A,the tensile strength of AZ31 magnesium alloy is 194 MPa,the yield strength is 89 MPa,the elongation is 14.8%,these parameters are increased by 23.6%,20.3% and 57.5% respectively compared with the natural solidification state.When the stirring frequency is 10 Hz,the tensile strength of AZ91 magnesium alloy is 164 MPa,the yield strength is 99 MPa and the elongation is 5.1%.These parameters are increased by 21.5%,19.3% and 41.7% respectively compared with the natural solidification state.