Research On External Field Assisted Forming Mechanism Based On 2D Continuous Dislocation Model

In the process of metal plastic deformation,the dislocation configuration distribution on the mesoscopic scale is related to the nature of the metal and the deformation conditions.Due to the difficulty of measurement,it is difficult to directly observe the dynamic distribution of dislocations during the deformation process.The continuous dislocation dynamics method uses dislocation density as the research object,which can not only predict macro material parameters such as flow stress,but also obtain material micro information such as cell size and dislocation density,which is an effective method for studying dislocation configuration.As a new material processing technology,external field assisted forming can improve the forming quality of materials,especially in the field of microplastic forming.Common external field processing methods include ultrasonic vibration,external electric field and external magnetic field.At present,there are few studies on the microscopic mechanism of the external field,and it is difficult to quantify.And by establishing a dislocation density model,studying the configuration distribution and mechanical properties of dislocations under the action of external forces and external fields can provide a theoretical basis for the application of electric,ultrasonic vibration and magnetic fields.The domestic research on continuous dislocation model mainly focuses on the evolution process of one-dimensional dislocation model or qualitative analysis of cell size,while one-dimensional model cannot reflect the distribution and configuration evolution of dislocation density in space.The two-dimensional dislocation configuration under the action has been researched to some extent,but there are few systematic studies on the effect of electric and external magnetic fields on the dislocation configuration distribution.Based on the theory of dislocation dynamics,a two-dimensional continuous dislocation dynamics model was established by studying the interaction of dislocation microelements.According to this model,the deformation of pure aluminum at a constant strain rate of 400 ° C was taken as the research object.The evolution of dislocation density,dislocation configuration,and flow stress with time was simulated,and the formation of various dislocation patterns during the deformation process was analyzed.The results show that the larger strain rate will increase the material flow stress and dislocation density,and strengthen the dislocation wall structure and refine the dislocation cell structure.The reliability of the model is verified by comparison with experimental data in the other literature.Based on this,the effects of the application of ultrasonic vibration,directional electric field and magnetic field are considered.The simulation of the dislocation configuration evolution is used to quantitatively predict the principle of ultrasonic softening,electroplasticity and magnetoplastic.The results show that the flow stress,dislocation density and cell size of the material will decrease after the external field is applied.