| With the increasing demand of lightweight automobile,the application of aluminum magnesium and other light alloy on car will become more and more.The traditional welding technology has a great limitation on the joining of dissimilar metals such as aluminum/ steel.The magnetic pulse welding technology is a new type of solidphase welding technology,which can efficiently obtain the dissimilar metal welding joint with excellent quality,and can effectively solve the welding problem of the aluminum magnesium alloy and other metals of the automobile body.The paper selects 5052 aluminum alloy and HC420 LA high-strength steel commonly used in automobile as research object,and carries out numerical simulation,process test,micro-analysis and fatigue performance test.The main research contents are as follows:Firstly,the Johnson-Cook constitutive model of 5052 aluminum alloy was established by quasi-static and high-speed tensile tests.A new magnetic pulse welding model is established based on the finite element and boundary element,and the magnetic pulse welding process of 5052Al/ HC420 LA under different process parameters is simulated.The distribution of induced current and electromagnetic force of flying plate is studied.The effect of different process parameters on the flying plate of electromagnetic field and collision speed was analyzed.The results show that the induction current of the flying plate is mainly concentrated in the center of the lapping area of the flying plate,and two connected rectangular loops are formed in the overlapping area of the flying plate.At the same time,it is found that the velocity difference of the flying plate in the direction of the welding seam is relatively large,and the speed difference in the direction perpendicular to the weld seam is small.The influence of different process parameters on the collision speed of flying plate is great.When the discharge energy is constant,the initial interval changes from 1.0mm to 1.8mm,and the collision speed of the flying plate varies greatly.When the initial interval is constant and the discharge energy changes from 25 kJ to 40 kJ,the impact velocity of the flying plate is relatively small.Secondly,the magnetic pulse welding test was completed under reasonable process parameters selected by pre-test and the acceleration course of the flying plate was reconstructed by PDV velocimetry system.The influence of discharge energy on the quality and microstructure of welded joint was studied by means of quasi-static mechanical performance test and micro-interface analysis.The results show that the strength of the welding joint increases with the increase of the discharge energy,and the welding joint exceeding the strength of the parent material is obtained when the discharge energy reaches 40 kJ.The PDV test results show that the collision speed of the flying plate increases linearly with the increase of the discharge energy.The microanalysis results show that the aluminum/ steel welding interface has an unwelded region,a straight region and a waveform region,and an Al/ Fe mixed transition layer is present in the waveform region accessory.At the same time,since the energy reaches 40 kJ,the waveform changes from the sine wave to the shear wave.The partial waveform of the shear wave is cut out,and the wave height is reduced.Therefore,the wave height first increases and then decreases with the increase of discharge energy.Finally,the fatigue performance test of magnetic pulse welding joints under different discharge energy was carried out.The effect of discharge energy on fatigue property of welded joint was studied.The failure mechanism of welded joint was studied by analyzing the failure mode and fatigue fracture of the joint.The results show that the fatigue strength of the welded joint increases with the increase of the discharge energy.At the same time,it is found that the displacement of the welded joint is stable during most of the fatigue cycle,and there will be a large displacement variation only at the end of the fatigue cycle,indicating that the Al/ Fe magnetic pulse welding sample has no obvious defect,And the most of the fatigue cyclic loads are used to produce initial fatigue cracks.The fatigue failure mode and micro fracture of welded specimens were analyzed.It is found that when the load level is higher,the welded joints are all in failure of the weld line due to the existence of brittle phase.As the load level decreases,the fatigue strength of the weld is gradually close to or higher than the fatigue strength of the aluminum alloy,and the failure mode is changed from weld failure to hybrid failure or parent metal failure.However,when the discharge energy(less than 30kJ)is small,the location of failure is located in the weld line due to the rapidly decreasing performance of the welded joint. |
