Effect Of Electropulsing Treatment On Microstructure And Mechanical Properties Of Deformed Magnesium Alloys

Due to the energy crisis and human needs diversification backgrounds,Magnesium alloy,the lightest metal structure materials,rich in natural resources,is attracting more and more attention.However,magnesium alloy plasticity is poor,and its strength is also low at room temperature,which limits its application.According to the classical metallic principle,grain refinement can not only improve the plasticity of the materials,but also can improve the strength of the material.Therefore,this paper attempts to improve the performance of magnesium alloy by grain refinement.Electropulsing treatment(EPT)is a new processing technique,which has the advantages of high input energy and high efficiency.In recent years,the application of EPT to improve the metal microstructure research has achieved good results.In this paper,AZ31 B magnesium alloy with variable rolling deformation was treated by EPT.Firstly,by controlling the experimental parameters of rolling deformation at room temperature,pulse width and treatment time,effect of EPT on the microstructure(recrystallization fraction,average grain size),the surface temperatures and the mechanical properties of samples were investigated by orthogonal test.Secondly,by controlling the pulse width,the recrystallization transition process of the sample was observed,and the thermal and nonthermal effects of EPT on the nucleation and growth ofrecrystallized grains were theoretically analyzed while the recrystallization mechanism of the deformed magnesium alloy was studied.Effect of rolling deformation and pulse width of EPT on the recrystallization fraction is significant,and the recrystallization fraction increases obviously with the increase of rolling deformation and pulse width.As a comparation,effect of the treatment time of EPT on recrystallization fraction is relatively smaller.Moreover,the rolling deformation has a greater influence on the average size of the recrystallized grains than the pulse width and treatment time of EPT.In addition,the thermal effect of EPT is mainly relative to the pulse width and the rolling deformation.With the increase of the pulse width and the rolling deformation,the Joule heat rises sharply,while the temperature of samples rise first and then maintain stable after a peak value with the increase of the treatment time of EPT.Finally,the optimal parameters for the best microstructure are 38% of the rolling deformation,70 ?s of the pulse width and10 min of the treatment time,under the conditions of which the average grain size of sample was reduced from 140 ?m to 6.8 ?m.The mechanical properties of the sample with 38% rolling deformation are very low due to the internal microcracks caused by excessive deformation.But the mechanical properties of the suboptimal parameter sample(30% rolling deformation,pulse width 70 ?s,treatment time 10 min)are excellent with tensile strength of 341 MPa and elongation of 11.6%.With the increase of pulse width,the locations where the recrystallization occurs follow a sequential order as follows: Twin,grain boundary,grain interior and then growth of the recrystallization grains.The recrystallization mechanism analysis shows that EPT promotes the recrystallization by thermal effect and nonthermal effect,and the nonthermal effect is the main reason to promote recrystallization,which reduces the recrystallization nucleation barrier and the atomic diffusion activation energy,therefore accelerates the recrystallization by improving the recrystallization nucleation rate.