Study On Friction Stir Welding Process Properties And Flow Characteristics Of Ultra-thin Copper And Copper Alloy

Copper and copper alloys have good electrical conductivity,thermal conductivity,ductility and corrosion resistance,and their micro-connections are widely used in aviation,electronics and energy technology.However,due to the high softening temperature of the welded workpiece,the different physical properties of the material,the reduction of frictional heat generation due to the reduction of plastic metal in the weld zone of the thin plate,and the fast heat transfer rate due to the increase of the specific surface area of the thin plate,the welded workpiece Local heating to a plastic state is more difficult,resulting in insufficient fluidity of the plastic metal,which brings problems such as poor weld formation and poor joint performance.Therefore,it is particularly important to study the evolution of grains in various regions of the weld and the mechanism of metal flow behavior.With reference to the research on micro stir friction welding by existing scholars,combining the characteristics and process characteristics of copper and copper alloy ultra-thin plate materials,the material and shape of the tool suitable for welding are selected and designed.The tool is made of WC-Co hard alloy material,which is composed of a concave 3°shoulder and a conical stirring pin.Under the same welding conditions,the buttμFSW process of 0.6 mm thick copper and copper alloy ultra-thin plates were achieved by using a tool with shoulders of 6 mm and 8 mm.The research shows that the welding heat input has a significant effect on the surface forming and mechanical properties of the joint.The use of appropriate tools and process parameters can obtain a well-formed and excellent joint.For H62 brass joints,the joint forming and tensile strength obtained with a shoulder of 8 mm is generally better than that of a shoulder of 6 mm.The mechanical properties of the joint are the best when the speed is 12000 rpm and the welding speed is 240 mm/min.The tensile strength can reach 370 MPa（about 92.5%of the base metal）,the micro hardness of the cross section of the weld is"W"shape,the center hardness is about 19.5%higher than the base metal,and the tensile fracture is at the hardness value In the low area,the fracture forms are all ductile fractures.For T2/H62 joints,the joint surface formed with a shaft shoulder of 8 mm is generally better than the shaft shoulder of 6 mm.The softening phenomenon is more serious,so the tensile strength of the joint obtained with the shaft shoulder of 6 mm is high.When the speed is 12000 rpm and the welding speed is 280 mm/min,the tensile strength of the joint is 82.6%of copper.Due to the material properties the different and brittle phases Cu₅Zn₈,AgZn₃,and AgZn exist at the metal interface,which makes the hardness value fluctuate slightly.No matter whether the same material or different materials are butt jointed,the average tensile strength of the joint will increase and then decrease with the increase of welding speed or speed.Based on the optimization of the tool and process parameters,the H62 butt joint obtained with a shaft shoulder of 8 mm was selected,and the macroscopic morphology of the joint and the evolution of the microstructure of each region under different process parameters were studied in depth.Changes in grain shape and size in various regions;T2/H62 butt joints obtained with 6 mm shoulders were used to analyze the rule of influence of weld metal flow behavior and process parameters,which is helpful to understand the formation of weld defects and the welding process The evolution of the microstructure and the optimization of welding parameters provide a theoretical basis for obtaining beautifully formed and excellent joints.It is obviously different from the traditional high-speed ultra-thin plate joints in that the joints have undergone rapid heating and cooling processes,HAZ,TMAZ,and NZ have obvious interfaces in the weld zone,and the grain shape and size of NZ are both horizontal and vertical There is unevenness.Changing the process parameters has a significant effect on the grain size of each micro-region of the joint.When the rotation speed is low or the welding speed is high,the welding heat input is low and the grain size is relatively small.Conversely,when the heat input is increased,the temperature at the weld seam rises quickly and high,and the plastic metal is softened to a high degree.The grain size of the regions will increase in different amplitudes.The flow behavior of the weld metal during the welding of ultra-thin plates of dissimilar materials was studied.Due to the differences in process parameters and metal flow speed,a clear interface of the metal flow occurred at the weld.Different from conventional thick plates,the thin plate has a small temperature gradient and strong stirring and squeezing action.When the ratio of speed to welding speed n/v is appropriate,the metal near the shoulder and stirring pin action area preferentially migrates and concentric vortex.Flow,the amount of metal（softer）on the retreating side of the weld migrates to the advancing side and flows upward.There is no excessive migration of the plastic material in the heat engine affected zone on the advancing side,and the metal at the bottom of the weld zone is more fully stirred and migrated.In order to study the characteristic changes of the temperature and force at the weld seam during welding of ultra-thin plates,the tool with a shoulder of 6 mm and 8mm was selected.The temperature,axial and transverse forces were collected,and the changes in temperature and welding force during the welding process were compared and analyzed.Under the same process parameters and different tool conditions,the changes in temperature and welding force are roughly the same.Stable axial and transverse forces can provide the heat input required for welding.