A Study On Deformation Mechanism Of WE43 At High Temperature And High Strain Rate

As the most widely used Mg-RE alloy in commercial application,WE43 can be widely used in aerospace,automotive and many other fields.However,many studies have focused on quasi-static conditions at present,with a lack in systematic research on mechanical properties and deformation mechanism of WE43 at high temperature and high strain rate.In addition,the elastic data obtained through experiment under high strain rate are not accurate due to the limitations of the testing methods.The elastic modulus of metal materials is different under various conditions,and few scholars have focused on this point yet.Therefore,this paper studied the mechanical behavior of as-cast WE43 and rolled WE43 which are widely used under various temperature and high strain rate.The deformation mechanism were analyzed by SEM and EBSD.Dynamic mechanical analyzer(DMA)which was used to predict the elastic modulus of WE43 at various temperatures and strain rates,was combined with the modified Johnson Cook model,to construct a new stress-strain constitutive model.Providing a theoretical basis for the application of WE43 in the automotive field and aerospace field.It is found that the mechanical properties of WE43 at low strain rate are different from those at high strain rate by conducting impact tests at 0.001/s,0.01/s,900/s,1400/s and 2000/s on as-cast WE43 and rolled WE43.The strain rate sensitivity of WE43 is small under low strain rate for the reason that the plastic deformation mechanism of as-cast WE43 and rolled WE43 is twinning,which is dominant in both cases through microstructure analysis,and dislocation slip.Under the condition of high strain rate,a large amount of stress is accumulated in the material due to high strain rate impact,and the accumulated stress gradually activates the non-basal plane dislocations which are difficult to start at room temperature.Furthermore,due to the addition of Y element in WE43,the CRSS of non-basal plane dislocation slip decreases greatly.Therefore,with the increase of strain rate,the amount of dislocations in WE43 increases significantly,while twins are limited.Above all,The plastic deformation mechanism of WE43 in two conditions gradually changed from twinning dominant to dislocation slip dominant.It is observed that thermal stress softening occurs in all samples with the increase of temperature under 1400/s strain rate at four temperature points of 100℃,200 ℃,250℃and 300℃.The number of twins decreases sharply with the increase of temperature,which can be explained by the high correlation between the CRSS of non-basal plane dislocation slip and temperature.The inhibited forming conditions of twins,and the consumption of twins coordinating plastic deformation makes the plastic deformation mechanism of WE43 change from twinning to dislocation slip under high temperature and high strain rate.In addition,dynamic recrystallization occurs in the rolled WE43 at high strain rate.The recrystallization bands gradually grow and merge into adiabatic shear bands with the increase of temperature.In order to obtain a more accurate elastic modulus of WE43 magnesium alloy,a dynamic thermomechanical analyzer was used for further research.It’s observed that the storage modulus of WE43 changed with the temperature and frequency.By using time-temperature superposition(TTS)principle,the storage modulus is translated into the main curve in a wider frequency range of a temperature point,and the storage modulus is converted into the elastic modulus in the time domain.Coupled with the temperature,the three-dimensional surface of temperature-strain rate-elastic modulus is drawn,and the elastic modulus of the material in a wider range of temperature and strain rate is obtained.By modifying JC model,the plastic deformation curves of WE43 at high temperature and high strain rate were obtained.The complete stress-strain curves of the material under various test conditions were obtained by integrating the predicted elastic modulus with the modified JC model.