Effect Of Electro-magnetic Field On Microstructure And Properties Of Industrial Pure Nickel Laser Welding

Due to the influence of low thermal conductivity and low nucleation rate of pure nickel materials,laser welding of industrial pure nickel will cause coarse grains inside the weld seams,which will seriously affect the corrosion resistance and mechanical properties of welded joints.The electro-magnetic stirring technology has the function of stirring pool,refining grain and improving performance.In order to explore the effects of different electro-magnetic field parameters on the microstructure and corrosion resistance of pure nickel weld seams,the microstructure and electrochemical corrosion behavior of pure nickel Ni201 laser welded joints under different electro-magnetic field parameters(magnetic field intensity,magnetic field frequency and electric field intensity)were studied in this paper.It provides reference data and technical support for the industrial application of electro-magnetic field assisted laser welding technology.This paper takes industrial pure nickel Ni201 which is commonly used in the nuclear power field as the research object,and bases on industrial high-power CO2 laser welding equipment and self-made transverse rotating permanent magnet electro-magnetic stirring device as the research means.Microstructure of welding seam,grain size,microhardness and the corrosion resistance of welding joints were analyzed by the metallurgical microscope,scanning electron microscope,microhardness tester,electrochemical workstation and other equipments.The conclusions are summed up through the data: Electro-magnetic field assisted laser welding can effectively reduce the grain size and improve the corrosion resistance of welded joints.In the magnetic field intensity range of 30~70mT,the stronger the magnetic field intensity,the better the grain refinement effect,and the better the corrosion resistance of the weld seam.In the magnetic field frequency range of 200~600r/min,the bigger the magnetic field frequency,the better the grain refinement effect,and the better the corrosion resistance of the weld seam.When the magnetic field intensity is 70 mT and the magnetic field frequency is 600r/min,the average grain size is 9.1μm and the self-corrosion current is 5.78μA,which is reduced by 11.1% and 24.6% compared with the laser welding.Adding an electric field to the molten pool on the basis of magnetic field can further refine the grains.The circuit voltage which generates the electric field in the range of 20~60V,the larger the circuit voltage,the better the grain refinement effect,and the better the corrosion resistance of the weld seam.When the magnetic field intensity is 70 mT,the magnetic field frequency is 600r/min and the circuit voltage is 60 V,the average grain size is 8.4μm,and the self-corrosion current is 5.23μA,which is reduced by 17.6% and 28.0% compared with the single laser welding.