Process And Joining Mechanism Of Magnetic Pulse Crimping With 6061 Aluminum Alloy To SPCC Steel Thin-walled Tubes

Lightweight is of great significance to the future development of our society.Starting from the diversity of materials,structures and processe s,the light-weighting design can realize the overall weight reduction of automobiles to a large extent,which can bring significant light-weighting effect.Considering the special requirements of strength and stiffness,various combinations of materials a re used,which involve the connection problem of tube fittings of dissimilar materials.As an efficient and environmentally friendly high-speed solid-phase joining technology,magnetic pulse connection technology is helpful to obtain reliable tube fitting joints.However,there are still difficulties in achieving reliable connections of thin-walled tube fittings with high joint strength.In this paper,numerical simulations,process tests,mechanical tests and microscopic analysis were carried out on magnet ic pulse crimping joints of thinwalled 6061 aluminum-SPCC steel fittings.The specific research content is as follows:Firstly,based on the crimping joint of 6061 aluminum-SPCC steel thin-walled tube fittings,the real magnetic pulse crimping process was simulated by numerical simulation method.The changes of electromagnetic field and structural field on the tube as well as the changes of stress and strain at the groove were analyzed in detail.It was found that the gap in the opening area of the discont inuous magnetic collector would cause magnetic flux leakage,which in turn led to uneven electromagnetic force distribution.A suitable groove gap reserved enough distance for the outer tube to accelerate,so the deformation was mainly concentrated in the groove area.The current density,magnetic field strength and electromagnetic force distribution on the tube changed as the deformation increased.When the groove depth was constant,the higher the discharge energy,the greater the speed of the outer tube accelerating into the groove of the inner tube.The greater the impact force on the inner tube,the greater the corresponding speed obtained.And with the crimping depth continued to deepen,the more obvious the deformation of the final crimping zone,the stress and strain were concentrated on the edge of the groove.Secondly,the groove depth suitable for magnetic pulse crimping joint of thin-walled tube fittings was determined through process test combined with mechanical property analysis,and further ex ploration of discharge energy parameters were carried out under the determined groove depth.The results showed that when the preformed groove was too deep,the inner edge of the groove would be torn and the joint structure would be defective when the crimping to certain depth.However,when the preformed groove was too shallow,the mechanical properties of the joint would be reduced.Therefore,increasing the groove depth within a reasonable range could improve the strength of the mechanical locking struct ure and thus improve the joint performance.For a thin-walled tube with a thickness of 1 mm,the best groove depth was determined as 2.0 mm.By comparing the PDV velocity with the numerical simulation results,it was found that the velocity-displacement curves matched well with a threshold of3.43%,which verified the accuracy of the numerical simulation.Finally,through mechanical performance testing combined with failure analysis,the impact of discharge energy on joint performance was explored.The thin ning and hardening of the crimping area was observed through deformation profile and micro hardness analysis,which revealed the connection mechanism of crimping joints of thin-walled tube fittings containing grooves.The results showed that the joint fail ure occurred at different energies,manifested by pulling off or twisting out of the groove area.With the increase of discharge energy,the mechanical properties of tube joints showed a trend of increasing and then decreasing,with the strongest mechanica l capacity of the joint at 16 k J energy.When the energy was low,the relative deformation of the steel outer tube was small,and the supporting force was stable.With the increase of the discharge energy,the thinning and hardening degree of the aluminum inner tube increased,the overall crimping depth increased,and the joint strength increased.When the energy was higher,the relative deformation of the steel outer tube increased significantly.At this time,the steel outer tube was unstable,and the deg ree of thinning and hardening of the aluminum outer tube decreased compared with that at low energy,which had a negative impact on the joint performance.Although the crimping depth continued to increase,the joint strength reduced.