| The aluminum-lithium(Al-Li)alloys,which are characterized with lower density,higher specific stiffness,excellent mechanical properties,and enhanced weldability as compared with conventional aluminum alloys,have been considered one of the most competitive lightweight structural materials for application in aerospace sector.However,the forming process of most Al-Li components need to be carried out at high temperature due to the poor plasticity of the alloys at room temperature.Therefore,the advanced elelctropulsing assisted forming process may be employed as an alternative to conventional hot forming route to approach the target of energy-saving,high efficient and green manufacturing.In this present study about 5A90 AlLi alloy,electropulsing assisted heating was applied for heat treatment and hot forming in order to realize the ageing treatment,grain structure and high temperature mechanical properties optimization,and stamping forming of typitcal parts of the 5A90 Al-Li alloy.Additionally,electropulsing assisted forming and ageing hardening of the 5A90 Al-Li alloy would be integrated together to approach the target of shape forming and properties improvement of the part.The electropuling assisted ageing(EAA)of the 5A90 Al-Li alloy was carried out.Results showed that during EAA,the precipitation and coarsening of the ?? strengthening phase were both enhanced due to the combination of the electromigration offering another ?? precipitate growth coefficient and the enhancement of diffusion due to the interaction between the vacancies and drift electrons,which played an critical role in shortening the ageing time and lower the ageing temperature for reaching the peak ageing temper of the 5A90 Al-Li alloy.Besides,based on the diffusion kinetics mechanisms and electro-migration theory,the coarsening kinetics equation of the ?? phase during EAA was presented out.Under the peak ageing temper,the strength of the alloy increased remarkably,but at the expense of ductility due the easy occurrence of strain concentration caused by the planar slip during deformation.The recrystallization behavior and corresponding mechanical properties of the cold rolled 5A90 Al-Li alloy was systematically studied based on the electropulsing assisted recrystallization annealing(EARA)of the 5A90 Al-Li alloy.It was shown that the climb of dislocations could be dramatically promoted by the electropulsing at high temperature,which resulted in the rapid transformation from cold rolled structure to recrystallized structure with fine grains,near-equiaxed grain shape,and weak crystallographic texture.After the subsequent EAA treatment,more excellent mechanical properties with outstanding combination of strength and ductility of the 5A90 Al-Li alloy could be achieved.According to the further theoretical analysis,the promotion effect of electropulsing on the dislocation climb was primarily due to not only the higher diffusion coefficient of vacancies under the application of electropulsing but also the another diffusion flux of vacancies induced by electromigration.In addition,the equation of the dislocation climb velocity was derived based on the diffusion theory and electro-migration.The high temperature deformation behavior of the 5A90 Al-Li alloy during conventional high temperature tensile and electropulsing assisted tensile(EAT)were studied.It was shown that not only the strength decreased dramatically,but also the elongation increased remarkably when the alloy was deformed at high temperature,and the elongation would further increase as the original grains were fined.During EAT,there was a more obvious decrease in strength as compared with conventional high temperature tensile,however,a sharp drop in elongation occurred due to the localized high temperature in the necking region caused by the risi ng electropulsing density.Compared with the conventional high temperature tensile,besides the occurrence of the dynamic recovery and the discontinuous dynamic recrystallization,the transformation of low-angle boundaries to high-angle boundaries that accelerated by the promotion effect of electropulsing on the dislocation climb played another significant role in the softening mechanism of the alloy during high temperature deformation when the electropulsing was applied.The electropulsing assisted free bulging(EAFB)and electropulsing assisted capshaped part bending(EACPB)of the 5A90 Al-Li alloy were performed,achieving the target of integrated control of not only the microstructure,formability and high temperature forming,but also the electropulsing assisted forming and ageing strengthening.According to the results of the EAFB,it was indicated that the bulging capability of the 5A90 Al-Li alloy improved due to the refinement of grain structure.In particular,the deformation amount of the alloy treated by cold rolling with 66.7% reduction combined with 10 s of EARA exceeded 200% during EAFB,which meant that the alloy with fine grain structure exhibited excellent formability.During EAFB,the deformation mechanism of the alloy with fine grain structure was dominated by grain boundary sliding while the failure mode was mainly characterized by cavities aggregation.On the other hand,the results of the electropulsing assisted V-shape bending(EAVB)and the EACPB of the 5A90 Al-Li alloy showed that the electropulsing assisted high temperature forming technology could remarkably eliminate springback and improve forming precision of the parts,and the mechanical properties of the parts could be optimized to peak aging status after subsequent EAA treatment.As a result,the target of shape forming and properties improvement of the part was achieved simultaneously.Moreover,the polarity effect was further verified by the results of EAT and EAFB,and the corresponding explanation was given based on the so-called “electron wind” effect theory. |
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