Numerical Simulation Study On Electromagnetic Induction Heating Of Titanium Aluminide Alloys

TiAl-based alloys have great application prospects in the aerospace and automotive industries due to their low density,high specific strength,and good creep properties at high temperatures.In order to overcome its brittleness at room temperature,the microstructure of the alloys needs to be accurately controlled by heat treatment.However,Ti Al-based alloys tend to be chemically active and are easy to react with most media at high temperatures.As a non-contact heating method,induction heating has the advantages of no pollution,fast heating speed,high heating temperature and easy to control accurately,which provides a strong support for the purity of the Ti Al during the process of heat treatment and control of the microstructure.But the current research on the induction heating process is focused on the surface quenching of carbon steel or the heat treatment of the welded pipe with short heating time,low temperature and no request for temperature gradient which is different from Ti Al's induction heat treatment process.Here we systematically studied the effect of the inductor structure,power supply parameters,cooling method,etc.on the macro temperature distribution of Ti Al induction heat treatment at different stages,which provides a theoretical basis for the induction heat treatment process.Firstly,this article establishes the model of temperature field of the induction heat treatment process with necessary simplification,and overcomes the difficulty of the constantly changing model during the movement of the workpiece through the method of multi-step arrangement and the suppression and activation of elements,realizing dynamic simulation of Ti Al induction heat treatment during the movement of hot zone.The general law of the temperature distribution of induction heating is analyzed.The center of the hot zone is basically coincident with that of the coils.There is a region with high temperature gradient at the position of the adjacent hot zone.In the radial direction,there is a lateral cooling area about 3?5mm deep on the outer surface of the workpiece.And the temperature distribution in the middle of the workpiece is more uniform.The steady-state temperature field under different sensor structures is simulated and analyzed.The simulation results show that the uniformity of the temperature field generated by the single-turn coil is poor.When the coil and the coolant are gradually away from each other,the maximum temperature gradient in the workpiece decreases,and the width of the area where the phase transition temperature area coincides with the high temperature gradient area increases.The advantage of the plane inductor is that it has an aligned concentrated heating effect.The disadvantage is that the heating interval is short and the eddy current loss caused by the coils is high.The temperature field analysis of single-turn coils with different cross-sectional dimensions show that the profile of the current penetration layer of the magnetic field generated by coils with a higher height tends to be flat,the uniformity of the generated temperature field is better than that caused by coils with a low height;The influence of the cross-sectional shape on the induction heating effect is weak;when the coil turns increase,the eddy current distribution on the workpiece surface changes from a continuous distribution to a two-segment distribution,and the superposition of magnetic field gradually weakens.During the heating process,the internal temperature difference of the workpiece gradually decreases.The width of the matching area determined by the temperature and the temperature gradient is elongated;when the frequency is increased,the thickness of the lateral heat dissipation layer of the workpiece will decrease;the temperature distribution of objects with different cross-sectional shapes is basically the same.But the temperature gradient inside the rectangular cross-section workpiece is radial due to the larger contour size,and the internal and external temperature gradients are large,which is not conducive to tissue control.The static and dynamic simulation results when the hot zone moves are analyzed and compared.The transient temperature in the center of the hot zone cannot reach the steady-state temperature distribution when hot zone movement speed is from 5mm/min and 10mm/min.Natural cooling occurs during the upward movement of the hot zone.When the moving speed increases from 1mm/min to 10mm/min,the cooling rate increases from 0.219?/s to 1.86?/s.The process of air cooling can be divided into two stages.The main difference is that the early cooling rate is faster,and the position of hot zone doesn't change.The measurement results of temperature field and magnetic field show that the magnetic flux density distribution obtained by numerical simulation and experimental measurement shows good consistency,but the measured data of the temperature field at the edge of the hot zone is higher than the simulation result,which is because the coefficient of thermal conductivity of Ti Al is smaller as the temperature decreases,slowing down the trend of temperature decrease.