Ultrasonic Vibration-assisted Plastic Deformation Behavior And Application In Riveting Process

Ultrasonic vibration plastic forming technology has been widely concerned and has been developed in various plastic forming processes such as wire drawing,extrusion and drawing.Because it can reduce forming force,reduce surface friction,improve surface forming quality,increase material forming limit,and promote deformation.At present,China has made great progress in the field of aerospace.Riveting technology has attracted much attention because of its important role in the connection of aircraft structures.With the large-scale application of large-diameter titanium alloy and aluminum alloy rivets for aviation,traditional riveting methods have been difficult to overcome the deformation resistance and meet the riveting interference fit standard.The application of ultrasonic vibration assisted plastic forming technology to the riveting process is expected to reduce riveting force,promote plastic deformation,improve riveting interference,increase riveting strength and promote the development of riveting technology and the progress of aviation in China.However,the mechanism of ultrasonic vibration plastic deformation is complex and the mechanism of action is still unclear.At present,the ultrasonic vibration plastic deformation mechanism of titanium alloy and aluminum alloy used in aviation is rarely studied.Ultrasonic assisted riveting technology is still in the initial stage of exploration and further research is needed.In this paper,Ti45Nb titanium alloy and 2A10 aluminum alloy used in aviation rivets are selected as research objects.In order to solve the above problems,the behavior and deformation mechanism of ultrasonic vibration-assisted plastic deformation were studied by ultrasound-assisted compression test.The ultrasonic assisted compression test was carried out with the ultrasonic vibration system on the universal testing machine,and the deformation behavior of the material in the ultrasonic loading process was analyzed.The mechanism of ultrasonic plastic deformation was studied by combining the results of microstructure characterization test(OM,SEM,EBSD,TEM),temperature change and hardness during compression.The ultrasonic assisted riveting test of titanium alloy and aluminum alloy rivet connecting 2A12-t4 aluminum alloy plate was carried out.The forming force of ultrasonic assisted riveting was studied.The microstructure of rivet heading was studied by metallographic experiment The ultrasonic vibration riveting quality was analyzed by measuring the diameter of the deformed rivet rod with an image measuring instrument and then calculating the interference.The riveting strength of riveting members obtained by different riveting methods was studied by the shear test of single rivet and double rivet.The result shows:Ultrasonic vibration can significantly reduce the flow stress in the deformation process of titanium alloy and aluminum alloy,and the decreasing amplitude is greatly affected by the ultrasonic loading time.The main reasons for the decrease of flow stress are ultrasonic stress superposition effect and ultrasonic softening effect.By analyzing the microscopic characterization data of the deformed material,it is concluded that ultrasonic energy is easier to be absorbed by crystal defects,promoting dislocation movement,accumulation and rearrangement,increasing dislocation and vacancy density,thus increasing the number of small-angle grain boundaries and the change of grain orientation,and improving the deformation capacity.In this paper,radial plastic deformation inconsistency occurs inside the compressed specimen and inside the rivet heading,and shear deformation occurs,forming a shear zone in which the grain deformation is severe.In aluminum alloy,because ultrasonic vibration provides energy for dislocation movement,the dislocation overcomes the hindrance of the second phase particles,increases the deformation degree of the small deformation zone,reduced the difference in the degree of deformation between the small deformation zone and the large deformation zone,alleviates the violent deformation of the shear zone to some extent,and makes the deformation more uniform.In titanium alloy,the areas with large deformation,such as large deformation zone,shear zone and central deformation zone,have a large number of crystal defects,and the deformation degree is greater under the action of ultrasonic energy.The deformation phenomenon assisted by ultrasonic vibration is opposite to that of aluminum alloy.In the ultrasonic assisted single rivet riveting test of titanium alloy rivet and aluminum alloy rivet connecting 2A12-T4 aluminum alloy plate:Under the action of ultrasound,the deformation force of rivet was significantly reduced,and the deformation force of titanium alloy rivet and aluminum alloy rivet rivet was decreased by 6.41%and 5.94%respectively.Compared with conventional riveting,the interference amount of titanium alloy rivet after ultrasonic riveting is increased by 1.76 times,and that of aluminum alloy rivet by 1.96 times.Moreover,ultrasonic riveting makes the interference amount distributed more evenly along the axis of rivet rod and has better connection performance.The shear strength of ultrasonic riveting is 2.45%higher than that of conventional riveting,it has better riveting performance.Double rivet riveting strength test:Ultrasonic riveting shear performance is better than conventional riveting,the shear strength of the double rivets arranged parallel to the shear direction is higher than that of the double rivets arranged perpendicular to the shear direction.This has certain reference value to the traditional riveting process.