Research On Laser High-speed Impact Welding Of Refractory Metals And Copper

At present,it is very difficult to realize micro-scale welding between refractory metals and copper without changing the structure of refractory metals and their alloys,which limits the application of refractory metals in industry.The laser high-speed impact welding process is a new type of solid-state welding process with very significant advantages in micro-scale welding.In this paper,the theoretical basis,the surface morphology of welding samples,the morphology characteristics of interface microstructures,the formation conditions,the formation mechanism and mechanical properties of refractory metals and copper in laser high-speed impact welding were studied by combining theory with experiment.The main research contents and results are as follows:Firstly,the interaction mechanism between laser and material during laser high-speed impact welding was studied;the shape characteristics of jet and interface wave at welding interface were discussed;the necessary conditions for the formation of welding interface were discussed;the theoretical model mechanism of the formation of welding interface wave was explored,which provided theoretical support for the experimental study of laser high-speed impact welding.Secondly,Mo/Cu welding samples were successfully obtained by laser high-speed impact welding under different laser energies.It was found by optical microscope(OM)that with the increase of laser energy,the springback of the welding center area became more obvious,and the surface wave of the welding sample also became more obvious.Further observation by scanning electron microscope(SEM)showed that with the increase of laser energy,the shape of the welding interface wave changed from straight to serrated.Through EDS analysis of the welding interface,it was found that the springback of the welding center area became more obvious at the welding interface.Weak element diffusion occurred on the surface.At the same time,there were no defects such as intermetallic compounds and small holes,which meant that laser high-speed impact welding is an effective way to realize Mo/Cu welding.The nanoindentation experiment showed that the hardness of nanoindentation increases more obviously and the increase of Mo was larger than that of Cu.The tensile shear test showed that the maximum tensile force increases with the increase of laser energy.There were two kinds of failure modes at the same time: welding interface failure and welding joint edge failure,and the failure occurred on the side of copper foil,which indicated that Mo/Cu welding joint had good mechanical properties.Finally,Ta/Cu welding samples was successfully realized by laser high-speed impact welding.The feasibility of Ta/Cu welding with different laser energy and flying distance was studied.It was found that the surface and bottom of Ta/Cu welding samples were plastic deformed to varying degrees without ablation and cracks under different process parameters.OM and SEM showed that the welding interface was circular.Besides,the welding direction was consistent with the direction of the interface wave peak offset on the side of Ta with higher density,and the waveform of the left and right welding areas were asymmetric.The effective welding area first increased and then decreased with the increase of flight distance,and increased with the increase of laser energy.The waveforms at different flight distances were wavy,and the amplitude and wavelength of the waveforms increased with the increase of flight distances.The waveforms at welding interfaces under different energy levels changed from flat to wavy with the increase of laser energy.At the same time,there were no defects such as intermetallic compounds and small holes,which meant that laser high-speed impact welding Ta/Cu is feasible.The hardness test of nanoindentation showed that the closer to the welding interface,the more obvious the increase of nanoindentation hardness value and the smaller the increase of Ta than that of Cu.In tensile shear test and peeling test,the main failure modes of Ta/Cu welding samples were: Welding interface failure and welding joint edge failure.It was found that the maximum tensile force and peeling force increase with the increase of laser energy,and increased first and then decreased with the increase of flight distance,which indicated that Ta/Cu laser high speed shock welding can obtain good quality welded joints.This study provides a new welding technology for the welding of refractory metals and copper,and provides theoretical and experimental guidance for the application of laser high-speed impact welding of refractory metals and copper in practical engineering.