Study On Connection Process Of Aluminum Alloy And CFRP Sheets Based On Magnetic Pulse Welding

With the globalization of the economy,the environmental pressure facing mankind is increasing.As one of the most important industrial products of human beings,it is essential to reduce fuel consumption and exhaust emissions.Therefore,the theme of automobile light weight is of great significance for achieving energy saving and emission reduction.The realization of lightweight mainly includes two aspects: lightweight of structures and lightweight of materials.It is one of the most effective ways to replace traditional steel materials by using new lightweight materials such as aluminum alloys,magnesium alloys,and carbon fibers.The use of multiple materials inevitably involves the problem of reliable joining of different materials.The magnetic pulse welding technology is an efficient,environmentally friendly and easy to realize automatic joining technology,which can realize the joining between metal and non-metallic thin sheets.This paper proposed a joining structure that uses electromagnetic pulse welding technology to realize the joining of aluminum alloy and carbon fiber sheets.It conducted research by the numerical simulation,process test,joints performance test and micro-morphology analysis.First,based on the LS-DYNA simulation software,the Al-CFRP joint structure of the sheet and the dimensions of welding coil,a numerical model coupled the electromagnetic field and the structural field was established.Through the FEM-BEM sequential coupling method,the changes of various physical quantities in the entire welding process were calculated.Using PDV equipment to measure the deformation speed under different discharge energy,and benchmarking with the simulation results,the error was within 10%.The distribution of current density,magnetic field strength and electromagnetic force on metal plates and coils were analyzed.The results showed that with the increase of discharge energy,the deformation speed of the metal sheet was faster and the electromagnetic force was greater.Then,four different types of Al-CFRP joints(single hole,horizontal double holes,vertical double holes and four holes)were used as test variables to conduct the tests separately.And the joints were tested for shear mechanical properties.It was found that different types of joints were different in the bearing load,energy absorption and failure mode.For horizontal double-hole and vertical double-hole structures,the peak load capacity was approximately equal,and the energy absorption effect of horizontal double-hole was significantly stronger than vertical double-hole.The failure modes of the two were also different.Two joints of the horizontal double holes failed at the same time,while the welds of the vertical double holes close to the inside of the carbon fiber board failed first.The joints of transverse double-hole fractures showed the pure shear failure,while the failure of vertical double-hole welding joints were different.The weld in inner hole showed an equiaxed dimple,and the weld in outer side showed a shear dimple.It showed that the stress state of the vertical double hole failure was different.And the failure mechanism of different types of joints was analyzed.According to the relevant conclusions of the tests,some design methods of Al-CFRP joints were proposed.Next,the micro-morphology test of the Al-CFRP joint could be welded at all three discharge energies.With the increase of energy,the waveform characteristics were more obvious,and the wavelength and amplitude were larger.Through microscopic observation of the interface between the two vertical joints,it was found that the shear occurred in the aluminum alloy sheet,and the hardness near the shear had increased to a certain extent,and the hardness in the non-shear zone hardly changed.The Al-CFRP-Al three-layer structure was tightly bonded,and the carbon fiber sheet had no failure modes such as fracture,delamination,and bending.It showed that the high-speed impact of the entire magnetic pulse welding process had not caused damage to the carbon fiber board.Finally,the connection mechanism of the Al-CFRP joint was revealed by the numerical simulation process.By extracting the relationship between collision speed and collision angle in the simulation process,the connection mechanism of the joint was obtained according to the welding conditions.The analysis found that the average collision velocity of the circular zones in the weld was lower than the average collision velocity of the straight area.According to the micro-topography characteristics of the Al/Al welding interface and the fracture at the two locations,it was proved that the welding strength of the straight zones was higher than that of the circular zones.