Research On The Process Parameters And Formation Mechanism Of Cracks Of Self-piercing Riveting For Dissimilar Metals

With the implementation of the energy conservation and emissions reduction,manufacturers in transportation industry,represented by aircraft and automobile,begin to use various new materials in order to realize the lightweight of fuselage and the car body.The traditional connections cannot meet the performance requirements of the joint,and SPR attracts tremendous attention with its unique advantage of mechanical connection,which has been widely used.Based on the SPR of aluminum and steel dissimilar metals,the article launches the research around the punch velocity and joint cracks.Based on the connection of 0.65 mm low carbon steel and 2mm 6000 aluminum alloy?0.65 mm low carbon steel and 2.5mm casting aluminum alloy,the article follows the design ideas of plates-rivet-dies to choose proper rivet and equipment for the joints.For the joint of 0.65 mm low carbon steel and 2mm 6000 aluminum alloy,the article analyzes the influence of punch velocity on formability of self-piercing riveted joints by the means of metallographic analysis,hardness test and mechanical test.The results show that with the punch velocity increasing,the changes of the peak force,kinetic energy of the equipment and the difference of strain rate are the main reasons that affect the forming performance of the joints.Punch velocities affect the work-hardening capacity of plates in the joints and interlock distance,consequently determining the failure mode of the joints in static strength tests.For the joint of 0.65 mm low carbon steel and 2.5mm casting aluminum alloy,the article makes the research on the forming mechanism of joint cracks.Observing the joint with the optical microscope and scanning electron microscope,the article analyses and summarizes the features and locations of the cracks.Also we analyze the deformation of the joint in the process of SPR using simulation.The results show that stress is mainly clustered in the tip of rivet leg and plates around the rivet,and high strain is mainly clustered in the places around the tip of rivet leg.The distribution and concentration places of stress and strain are just where cracks initiate and develop.Annealing heating treatment is used to enhance the deformation capacity of cast aluminum alloy before SPR process,finally eliminating the cracks in the joints.Annealing temperature are 520 ? and 550 ? with heated-up time of 2h,heat preservation time of 4 h and natural cooling in the furnace.The results show that when annealing temperature is 520?,the toughness and deformation capacity of cast aluminum alloy improves a lot and then macro and micro cracks in joints are effectively eliminated.