Research On Dissimilar Metal Foils Welding By Laser High-speed Impact Welding

In recent years,with the rapid development of microelectronics,medical devices,batteries and other industries,the demand for the joining of micro-materials with light,thin,short and small features is increasing in the manufacture of micro devices.The laser high-speed impact welding process has a significant advantage in the welding of dissimilar metal foils with small scale size and great melting point difference.Therefore,it has wide industrial applications.In this dissertation,the microstructure and its formation mechanism at the weld interface and the bonding mechanism of the dissimilar metal foils by laser high-speed impact welding was investigated through experimental study and numerical simulation.In addition,the dynamic response of the flyer plate and the base plate was revealed during high-speed impact welding.The main research work and conclusions are as following:Firstly,welding of Al/Cu using laser high-speed impact welding was carried out.The microstructure of the interface was observed and analyzed by scanning electron microscopy(SEM)and X-ray energy dispersive spectroscopy(EDS).It was found that the laser energy has significant effect on the morphology of the weld interface,in which the microwave interface was a kind of ideal interface and the wavelength and amplitude increases first and then decreases along the direction of welding.There was no obvious heat affected zone at the weld interface when the laser energy below 1200 mJ.However,there was local melting layer and melting block formed at the weld interface when the laser energy reached 1550 mJ.In addition,EDS analysis showed that weak interdiffusion occurred between Al element and Cu element near the weld interface.Secondly,a new laser high-speed impact welding method was presented,and welding of Ti/Cu by the method was carried out.SEM test showed that Ti/Cu weld interface was a typical microwave interface,and there was no defect such as heat-affected zone and intermetallic compound.Moreover,the wavelength and amplitude of the interface wave increased with the increase of laser energy when the pre-forming depth of the flyer plate was constant.EDS analysis showed that there was no significant interdiffusion between Ti element and Cu element at the weld interface,and the combination of Ti/Cu with different crystal structure was more difficult to diffuse than the combination of Al/Cu with the same crystal structure.The tensile shear test and the peeling test showed that the failure modes of the welding specimens were the fracture failure at the weld interface and edge of the weld spot on the flyer plate.In addition,metallographic analysis showed significant grain refinement at the weld interface,which in turn resulted in a significant increase in nanoindentation hardness at the weld interface.Finally,the numerical simulation of the welding of dissimilar metal foils by laser high-speed impact welding was carried out by using the smooth particle hydrodynamics(SPH)method.It was found that the SPH method reproduced the high-speed impact welding process,the impact jet at the collision point,the rebound of the flyer plate and the spallation behavior of the base plate.The jet was mainly derived from a thin layer of metal on the surface of the flyer plate.And the formation of the jet was an important condition for the solid state bonding between the flyer plate and the base plate.The impact velocity and the properties of the material have significant effect on the morphology of the weld interface.The weld interfacial wave was formed by the base plate being periodically penetrated by the flyer plate.The springback of the flyer plate caused cracking at the weld interface near the center of the joint.The base plate spalled under the impact of the flyer plate with high speed.The research of this dissertation could provide some theoretical and experimental value for the application of laser high-speed impact welding.