Research On Fiber Laser Welding Procees For The Zirconium Alloy Thin Sheet

Zirconium alloys are widely used in the nuclear power industry due to its excellent core performance, mechanical properties and corrosion resistance. Welding is an essential connection technology in equipment manufacturing of zirconium alloys, but in the laser welding process, Zirconium alloy sheet is extreme ly sensitive to laser energy and small changes in process parameters have a significant impact on the quality of welding, when more than 300 ?, Zirconium alloy is also easy to suck hydrogen, oxygen, nitrogen, gaseous impurities which sharply reduce the mech anical properties of weldments, so strengthen isolation weld and heat affected zone and develop a reasonable welding parameters is critical to obtaining good welding quality.This article aims to explore a new zirconium alloy welding technology to achieve high-quality zirconium alloy welding. Owing to the limitations of pulsed laser welding and vacuum electron beam welding, a continuous fiber laser welding process of zirconium alloy was presented, which was based on the advantages of small deformation, fast welding speed and good sealing property, etc. With 0.7mm thick Zr-Sn-Nb alloy sheet as the research object, the range of welding process parameters were determined by combination of theoretical analysis and single factor method. Based on this, the three factor five level regression orthogonal laser welding test was carried out. The relationship between the laser weld pool shape with process parameters is studied on the basis of the response surface method and laser welding process energy coupling behavior is analyzed through the research of welding cross-sectional area of the melting, to provide a basis for the development of laser welding temperature field simulation process parameters and the determination of heat source parameter.With ANSYS software for computing platform, a nonlinear 3-D transient heat conduction model was created by means of the finite element analysis, and a simulation research was performed on Zr-Sn-Nb alloy thin fiber laser welding process of 3-D transient temperature field. Fully considering the material parameters in thermal and physical properties of temperature correlation, protective gas forced convection, phase change latent heat and other factors. According to the laser energy coupling rule, the laser coupling efficiency is de bugged by using the trial and error method and the shape and size of the simulated weld pool are compared with the actual weld. By comparing and analyzing the temperature distribution cloud pictures, welding thermal cycle curve and the shape of the weld po ol, the relationship between the temperature field distribution where temperature is above 300 ? and the welding process parameters is studied and optimization of welding process parameters and the size range of the protection area are obtained on the basis of the welding model and simulation method is verified to be reliable. And the simulation results are verified by experiments. The result of optimization of the welding process parameters and welding need protection area size range can be used to provide a basis for the design of side protective device and the formulation of welding process.The autobiographic microscope and scanning electron microscopy(SEM) are used to observe the welding seam microstructure, phase composition and distribution, grain size and distribution. The welding pieces of micro-hardness and joint mechanical properties are tested by micro-hardness meter and electronic universal testing machine. It is found that there is no cracks, porosity and other defects within the weld, the main elements relative content have no obvious change compared with that of parent metal, the grain size range expanded slightly but no significant coarsening, and the tensile properties of the joint is close to that of the base material, and the fracture position is located in the base material. Based on the analysis and test results of the appearance morphology, microstructure and mechanical properties of the welded joint, the feasibility of the zirconium alloy laser welding technology explored in this article to be used in nuclear industry of the actual working condition was demonstrated.