Experimental And Numerical Research On Laser Impact Welding Of Ti/Cu Foils

As a novel solid-state micro welding process,laser impact welding can weld metal foils by single pulse laser.This dissertation realized the laser impact welding of Ti/brass two-layer foils and Cu/Ti/Cu three-layer foils for the first time.The welding process,process parameters,interface morphology,microstructure,bonding strength and welding mechanism were systematically investigated via experiments and numerical simulation.The main research contents and results are as follows:Firstly,the welding of Ti/brass two-layer foils was realized via laser impact welding.The influence of process parameters on the welding feasibility of Ti/brass was investigated.The surface and cross-sectional morphology,microstructure and bonding quality of the two-layer composite plate were investigated via optical microscope(OM),scanning electron microscope(SEM),energy dispersive X-ray spectroscopy(EDS)and tensile shear tests.Results indicated that the impact velocity and angle could be changed by changing the laser energy and standoff distance,and the welding effect was the best when the standoff distance was 0.2mm.The welding interface was distributed in a ring shape,the welding area increased with the increase in laser energy,and the initial unwelded area has a great influence on the welding area.The jet particles in the springback came from both the flyer Ti and target brass,and a5-?m-thick element diffusion layer occurred at the interface.The interface waveform size expanded along the welding direction,and increased with the laser energy.Increasing laser energy can improve the bonding strength of composite plate,and three different failure modes appeared in tensile shear tests.Secondly,the laser impact welding process of Ti/brass foils was simulated via smoothed particle hydrodynamics(SPH).Results indicated that the SPH simulation results were basically consistent with the experimental results,and the welding interface presented the characteristics of high plastic strain,shear stress,temperature and pressure.The jet near the collision point ejected outward at high velocity,and its source was related to the density ratio of the two materials.The generation of interface waveform was affected by the change of collision point position and the periodic change of jet ejection direction.The interface waveform size increased along the welding direction,which was determined by the change of horizontal welding velocity and normal stress.The increase in impact velocity,standoff distance or density ratio of flyer/target will expand the interface waveform size,while the increase in yield strength ratio of flyer/target will reduce the interface waveform size and delay the initial position of first waveform.The generation and expansion of springback and cracking were related to the peak position of normal stress.Finally,the welding of Cu/Ti/Cu three-layer foils was realized via laser impact welding.The influence of process parameters on the welding feasibility of Cu/Ti/Cu was investigated.The surface and cross-sectional morphology,microstructure and bonding quality of the three-layer composite plate were investigated via OM,SEM,EDS and tensile shear tests.Results indicated that the welding effect was better when the standoff distance was 0.2/0.2mm or 0.3/0.2mm.The interface morphologies of the upper and lower welding regions of the composite plate were different.Increasing the laser energy and standoff distance can expand the effective bonding area within the appropriate parameter range.The interface waveform presented discontinuous and multi-segment characteristics,and the waveform size of the upper and lower welding regions increased with the increase in laser energy under 0.2/0.2mm standoff distance.Element diffusion occurred at the interface,and local melting layer was found.Increasing laser energy improved the bonding strength of three-layer composite plate,increasing standoff distance caused the maximum tensile force to increase first and then decrease,and there were also three different failure modes in tensile shear tests.On the basis of enriching and improving the experiments and numerical simulation of two-layer metal foils welding,this dissertation systematically explored the welding feasibility of three-layer metal foils,in order to provide new research direction for laser impact welding,and provide theoretical basis and data support for the industrial production of Ti/Cu two-layer and three-layer composite foil plate.