| Automobile lightweight technology is an effective way to reduce automobile exhaust pollution.As a high-quality and lightweight material,aluminum alloy has been widely used in various automobile structures.However,when using traditional welding,aluminum alloy joints often have many defects such as pores,cracks,heat-affected zones,etc.,which lead to a decrease in joint reliability.Magnetic pulse welding technology is an efficient,green and environmentally friendly welding method,which can be effectively used in the connection of aluminum alloy materials and can significantly improve the quality of aluminum alloy welding.In this paper,AA5052 aluminum alloy sheet is used as the welding material,and a welding structure that can realize unilateral magnetic pulse spot welding is proposed to meet the requirement that the open parts of the automobile can only form a weld nugget on the inner plate.The weldability,mechanical properties,joint failure mode and microscopic connection mechanism of magnetic pulse spot welded joints under different process parameter combinations were studied through numerical simulation,process experiment and microscopic observation.A magnetic pulse spot welding torch head coil that can be assembled and matched with an industrial robot is designed.A magnetic pulse spot welding gun head coil that can be matched with an industrial robot is designed.The electromagnetic field distribution and force deformation of the magnetic pulse spot welding gun head and the plate coil are compared by numerical simulation.Finally,the structural parameters of the magnetic pulse spot welding gun head are optimized.Firstly,the numerical simulation of the new structure of AA5052 aluminum alloy thin plate magnetic pulse spot welding connection was carried out through Ls-dyna commercial finite element software.The distribution law of current,magnetic field and electromagnetic force in the numerical simulation of magnetic pulse spot welding,as well as the deformation and weldability conditions of the flying plate in the process of magnetic pulse spot welding are analyzed.The collision velocity error between the test results of the all-fiber laser Doppler velocimeter(PDV)and the simulation results is within 5%,which verifies the reliability of the numerical simulation.Simulation results show that the magnetic pulse spot welding process,the surface uneven current distribution in the coil,the induced eddy current produced on the surface of the fly plate is a two symmetrical closed loop,the induced current density increases and then decreases.According to the material flow limit theory of explosive welding,the collision speed required to achieve welding increases with the increase of the collision angle,so the weld is only formed at a suitable distance from the center point and is symmetrical about the center point.Secondly,the mechanical properties of AA5052 aluminum alloy MPW joints under different process parameters were tested through quasi-static tensile and cross tensile tests,and the performance differences under different failure modes of the joints were analyzed to try to obtain the best combination of process parameters.It was found that the joints with different process parameters have different load bearing and failure modes.With the increase of the welding gap and the pre-formed diameter of the flying plate,the peak value of the quasi-static tensile load of the spot welded joint first increased and then decreased.The magnetic pulse spot welded joint changed from the pull-out failure of the weld joint to the tear failure of the base material around the weld.The optimal welding gap and the pre-formed diameter of the flying plate under fixed energy are 1.4mm and 16 mm respectively.Then,under this parameter combination,the influence of the discharge energy on the quality of the magnetic pulse spot welding joint was explored,and it was found that the joint performance first increased and then decreased with the increase of the discharge energy.Finally,the best magnetic pulse spot welding parameters of AA5052 aluminum alloy are: H=1.4mm,D=16mm,E=36k J.Then,by observing the microscopic morphology of the cross-section of the magnetic pulse spot welding joint,it is found that the weld material has undergone obvious grain refinement,and the local material performance,hardness and strength have been enhanced.In the fracture of the quasi-static tensile test,there is base material adhesion,and there are equiaxed dimples and shear dimples at the same time.Finally,based on the magnetic pulse spot welding technology and the design principle of the plate coil,a magnetic pulse spot welding gun head coil suitable for welding various complex body structures is proposed.Using Ls-dyna commercial finite element software,a three-dimensional numerical model of the magnetic pulse spot welding gun head was established,and the structural parameters of the welding gun were optimized.Comparative analysis of the coil deformation shows that,compared with the flat coil,the magnetic pulse spot welding torch head coil has the significant advantages of flexibility,compactness,small deformation and long life.The optimization of the geometrical structure parameters of the coil found that the smaller the height of the middle arm of the coil,the better the welding effect of the magnetic pulse spot welding gun head coil.The cross-sectional shape of the coil was optimized for the void in the weld of the magnetic pulse spot welding joint.Comparing the simulation results of rectangular cross-section and circular cross-section coils,it is found that the use of circular cross-section coils can effectively solve the problem of unwelded voids between welds. |
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