Analysis Of Connection Mechanism And Connection Conditions Of Polycrystalline Pure Copper Cold Press Welding

Pure copper plays an important role in many industries because of its excellent conductivity,high strength and good ductility.In order to maintain its good functionality in the case of connection,solid-phase welding at room temperature has become an important option in this kind of material connection,and will have a broad application prospect.In this paper,the T2 polycrystalline pure copper material is taken as the research object,which is connected by butt cold press welding,and the plastic flow behavior and deformation mode of the material at the interface in the connection process are revealed by using its isotropic characteristics,combined with macro micro analysis and finite element simulation.A simple metal connection criterion based on strain is established,and then through the analysis of microstructure evolution,the real material is obtained Physical conditions of the existing cold press connection.These analyses will promote the application of polycrystalline pure copper cold pressing connection technology and the development of functional material connection theory.The main results are as follows:During butt cold press welding,when the extension length of the copper bar to be welded exceeds a certain value(l?8 mm),the pure copper begins to connect at the flash position,but not at the center position.This is because the metal plastic flow in the center of the die is constrained,and the metal flow in the flash position is more intense.By comparing the effective plastic strain distribution with the optical microstructure of the joint,the condition of cold press welding is judged.It is considered that the effective plastic strain of the contact interface can reach about 2.6 when the effective plastic strain of the contact interface reaches about 2.6.In order to verify the connection criterion,reduce the diameter of pure copper specimen for numerical simulation.With the decrease of the diameter,the high strain area expands to the center of the interface.When the diameter is 2 mm,the effective plastic strain of the whole interface is more than 2.6,which can realize the full interface connection.Based on the finite element numerical simulation of the deformation behavior of cold press welding,the EBSD analysis of the microstructure evolution of the joint interface was carried out,and the process of cold press welding of pure copper was studied.During the cold press welding of pure copper,with the increase of strain,the recrystallization fraction in the joint area increases obviously.It is considered that recrystallization plays an important role in the connection process of cold press welding of pure copper.This is because the strain induced grain boundary migration is the main nucleation mechanism during recrystallization.The grain boundary migration induced by strain makes a part of the large angle grain boundary raised during the process of large plastic deformation.The grain boundary migration is driven by strain storage energy,leaving a low dislocation content area behind the boundary.The increase of local temperature and the decrease of recrystallization temperature caused by severe plastic deformation will lead to the formation of new crystal structure at the interface,which will become recrystallization nucleation.With the increase of effective plastic strain,a large number of dynamic recrystallized grains begin to appear around the original grain boundary,and with the further deformation,the recrystallized grains gradually replace the original deformed grains to form a common grain at the junction interface,and finally realize the effective connection between the separated specimens.Because the temperature rise is not significant,the dynamic recrystallization grain size increases first and then tends to be stable with the increase of plastic strain.