Research On Technology And Numerical Simulation Of AA5052/HC340LA Electromagnetic Clinching-Bonded Joint

Under the background of automobile lightweight,aluminum alloy had been used more and more in automobile body because of its advantages such as light weight,low cost and high plasticity.Replacing steel plate with aluminum alloy could reduce the weight of body by about half,which was one of the effective ways to realize automobile lightweight.Clinching could realize direct connection between steel and aluminum.However,clinching joints had low static strength,low corrosion strength,poor air tightness and prone to electrochemical corrosion,which could not meet the strength requirements of body structure parts.Adding adhesive between the sheets could effectively improve the strength of the joint,enhance air tightness,and prevent electrochemical corrosion.Electromagnetic clinching technology had the advantages of fast riveting speed,high processing efficiency,better riveting effect and so on,which could obtain more stable and reliable joints.In this paper,the steel/aluminum structure electromagnetic clinching-bonded joint was taken as the research object,and the process experiments were carried out to explore the influence of process parameters on the forming and mechanical properties of the joints.The forming process,plastic strain of sheet metal,equivalent stress of sheet metal and the distribution of adhesive thickness after forming of the joint were analyzed by using the finite element method.The shear mechanical properties of the electromagnetic clinching joint,the bonded joint and the electromagnetic clinching-bonded joint under high-speed loading were investigated.Firstly,the effects of the thickness of the adhesive layer and the discharge energy on the electromagnetic clinching-bonded joint were studied from the aspects of the section morphology,the hardness of the joint and the quasi-static shear mechanical properties.The cross-section morphology and force-displacement curves of the joints with different process parameters were analyzed.The results show that the thickness of the adhesive layer and the discharge energy could affect the formation of the interlocking structure.The joint with the thickness of 0.2 mm and the discharge energy of 8.0 k J forms a good interlocking structure,and had good quasi-static shear mechanical properties and energy absorption properties.Secondly,a finite element model of the electromagnetic clinching-bonded joint was established to simulate the forming process of the joint with a thickness of 0.2 mm and a discharge energy of 8.0 k J.The accuracy of the model was verified by comparing the crosssectional morphology of the simulated joint with that of the test joint.The finite element model was used to describe the forming process of the joint and the variation of the thickness of the adhesive layer.The variation law of plastic strain and stress of the local characteristic unit of sheet metal with time during the joint forming process and the variation law of the thickness of the adhesive layer after the joint forming were studied.It is concluded that the plastic strain and stress of the characteristic element near the punch fillet are the largest,and the adhesive layer was the thinnest,which could provide guidance for the subsequent dynamic performance analysis.Finally,the dynamic performance of three kinds of joints was studied.By analyzing the force-displacement curves of the joints at different tensile velocities,it was concluded that the high-speed shear strength of the joints increased with the increase of the tensile speed.The strength and energy absorption of the clinching-bonded joint were obviously better than that of the single joint.The strength and energy absorption of clinching-bonded joints were significantly better than that of a single joint.The peak load at the three tensile speeds(1 m/s,5 m/s and 10 m/s)was increased by 322.9%,311.7% and 282.2%,respectively,compared with that of clinching joints.The energy absorption value was increased by 37.9%,39.1% and 39.8%respectively compared with the bonded joints.By analyzing the strain field and local strain in the lap zone of each joint,three kinds of deformation behaviors of joint sheet material under different tensile speed were obtained.Finally,the failure mechanism of each joint was summarized by analyzing the failure fracture.It was concluded that the failure area ratio of each failure mode was different under different tensile conditions,and the interface failure area was the largest.