Effect Of Pulse Current On Microstructure,Mechanical And Corrosion Properties Of AZ31 Magnesium Alloys

Magnesium alloys have received extensive attention in the automotive,aerospace and communications sectors due to their low density,high specific strength,and easy recycling.However,compared with other metal structural materials,magnesium alloys have poor plasticity at room temperature and can be corrupted easily,which severely limit their large-scale commercial application in various fields.Related studies have shown that applying pulse current to the metal deformation process can effectively reduce the deformation resistance and improve the formability of the difficult-to-deform metal.However,there are few studies on the influence of pulse current on the microstructure and properties of magnesium alloys.Therefore,in order to study the influence of pulse current on the microstructure and properties of AZ31 magnesium alloys,the tensile test under pulse current with different parameters has been carried out.The influence of pulse current on the microstructure,mechanical properties and corrosion performance of AZ31 magnesium alloys has been analyzed.The qualitative relationship of pulse current parameters-microstructure properties has also been discussed.The dynamic recrystallization mechanism of AZ31 magnesium alloys under the action of pulse current has been revealed.The main conclusions of this paper are as follow:(1)The tensile test of AZ31 magnesium alloys under the pulse current was designed and carried out.It was found that applying appropriate pulse current during the tensile process can refine grains,increase the elongation of AZ31 magnesium alloys,reduce its tensile strength and hardness,change its fracture mode,and improve the corrosion resistance of magnesium alloys.The degree of change in microstructure and mechanical properties is strongly dependent on the pulse current parameters.The average grain size and elongation both decrease first and then increase with the increase of pulse current parameters(pulse current density,pulse current frequency,duty cycle),while the tensile strength and microhardness decrease with the increase of pulse current parameters.Under the experimental conditions,the optimal parameters are combined with a current density of 20 A/mm~2,a frequency of 500 Hz and a duty ratio of 0.3.At this time the AZ31 magnesium alloys has the highest elongation up to~44.5%,the average grain size refine to 4?m,ultimate tensile strength(UTS)and yield strength(YS)are~174 MPa and~101 MPa,respectively,and the microhardness is~60 HV.The improvement of the corrosion resistance of AZ31 magnesium alloys can be mainly attributed to the occurrence of dynamic recrystallization by the introduction of pulse current,so that the structure is uniform and the dislocation density in the structure is reduced.(2)The temperature changes of AZ31 magnesium alloys samples with different pulse current densities were studied.The results show that the larger the pulse current density is,the larger the temperature increase is.The temperature of each sample reaches the maximum at the moment of fracture,and when current density is 0,15 A/mm~2,17.5 A/mm~2,20 A/mm~2,22.5A/mm~2 and 25 A/mm~2,the temperature at break is 23oC,123oC,180oC,209oC,256oC,and319oC,respectively.The thermal effect and non-thermal effect of pulse current promote the dynamic recrystallization of AZ31 magnesium alloys.Under the optimal combination of parameters,the dynamic recrystallization degree is the highest,and the recrystallization ratio can reach 95.3%.The maximum strength of the basal texture is 17.4 and 9.4 when tension under non-current and optimum current density,respectively.This texture weakening can be attributed to the occurrence of dynamic recrystallization of AZ31 magnesium alloys under pulse current.The thermal and non-thermal effects brought by the introduction of pulse current can promote the speed of dislocation climbing,which in turn increases the recrystallization nucleation rate,while the thermal and non-thermal effects also can reduce the energy required for nucleation of AZ31 magnesium alloys.The two points mentioned above are beneficial to promote dynamic recrystallization of AZ31 magnesium alloys,thereby improving the plastic deformation ability of AZ31 magnesium alloys.