| The laser impact welding(LIW)can realize the connection between the micro-scale metal foils.There is almost no heat-affected zone after welding and the weld results are reliable and stable.In this paper,Ti/SS and Cu/Al/Cu metal foils are weld by the LIW.The surface morphology of the welding samples,microstructure of the welding interfaces,mechanical properties of the weld joints and formation mechanism of the interfacial wave were studied.The main research contents and results of this paper are as follows:Firstly,the experimental research on LIW of Ti/SS metal foils was carried out.The surface morphology of the welding samples was observed by optical microscope.It was found that when selecting the appropriate laser pulse energy and standoff distance,the flyer plate can obtain good surface quality.The waveform of welding interface was observed and analyzed by SEM.The study shows that when the laser pulse energy or standoff distance is increased,the waveform of the welding interface transitions from a straight shape to a microwave shape,and finally transforms into a wave shape.EDS analysis showed that there was trace element diffusion at the welding interface and no intermetallic was formed.The hardness of the area near the welding interface was tested using a nanoindenter.The study found that as the distance between the test points and the welding interface increases,the hardness value obtained by the test decreases.The welding samples were subjected to tensile shear test by an electronic universal testing machine.It was found that increasing the laser pulse energy or standoff distance,the weld strength of the joints increased.Secondly,an experimental study on LIW of Cu/Al/Cu metal foils was carried out.The feasibility of LIW of three-layer metal foils is explored.The surface morphology of the welding samples was investigated.It was found that upper surface of the flyer plate at the center of the weld spot had a slight springback,and the surface of the weld area showed roughness and wrinkles compared with the unweld area.The microstructure of the welding interface was studied.The study found that when the laser pulse energy is small,a small discontinuous bonding area is observed at thelower welding interface.When the laser pulse energy is large,the existence of the melting zone is observed at the lower welding interface.The hardness test results show that after the experiment,the hardness of the flyer and the base plates increases with the decrease of the distance from the upper welding interface and the lower welding interface,respectively.The joint strength and failure mode of the weld specimens were studied by tensile shear test.It was found that when the laser pulse energy was increased,the bonding quality of the joints was improved.In the tensile shear test,there are mainly two failure modes: upper welding interface fracture failure and lower welding interface fracture failure.Finally,the smooth particle hydrodynamics method was used to simulate the LIW of Ti/SS metal foils.The simulation results can effectively reproduce the welding process,the impact jet and the cracking of the bonding interface near the center of the weld spot.The increase of impact velocity or standoff distance leads to an increase in the impact pressure and effective plastic strain at the interface,which in turn causes the interface waveform to change from flat to microwave to wavy.The formation mechanism of the interfacial wave is very similar to the theory proposed by Bahrani: The interfacial wave is formed by the periodic penetration of the base plate by the lower density flyer plate.The reaction force of the flyer plate by the base plate is greater than the bonding force between the two,which causes the bonding interface to crack.The cracking usually occurs in the region near the center of the weld joint.The research in this paper provides theoretical and experimental guidance for the engineering application of laser impact welding and a new method for the connection of three-layer plates. |
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