Technical Simulation And Experimental Study On Laser Lap Welding Of Three Layer Invar Alloy Sheet For LNG Ships

Invar alloy has become the main material for manufacturing thin-film liquid cargo tanks of LNG ships because of its advantages such as low expansibility.There are various types of weld joint thickness matching in the liquid cargo tanks of LNG ships,such as two or three layers of lap and stack welding form.Compared to two-layer welded joints,it is difficult to precisely achieve the technical requirements of weld penetration rate for three-layer plate welded joints in the actual welding process.In order to accurately achieve the technical requirements of penetration depth and improve the quality of weld in the LNG ships Invar alloy three-layer thin plate welding,this paper uses laser welding technology to research technical simulation and experimental study on laser lap welding of three-layer invar alloy sheet for LNG ships,and through the establishment of LNG ships Invar alloy three-layer thin plate laser welding process parameter library to improve welding efficiency,reduce the cost of trial and error in engineering applications.The primary research contents of this paper are as follows:(1)Establish a numerical simulation model to research the influence of different surface heat source power utilization and body heat source power utilization on the weld temperature field under the composite Gaussian heat source model,and discuss the impact of laser power and welding speed on the melt pool temperature and the back deformation of the weld;(2)Analyze the influence of different process parameters on the weld formation using single factor tests,and then design orthogonal tests to obtain the optimal process parameters for Invar alloy thin plate laser stack welding.(3)Compare the weld joint forming data and weld cross-sectional diagrams obtained under test and simulation to confirm the heat source model proposed in this paper;(4)Tset the weld quality of the welded workpiece under the optimal process parameters through weld surface formation,metallographic organization,mechanical properties,and penetration properties.The results show that:(1)Under the composite Gaussian heat source model,the power utilization rate of different surface and body heat sources can reflect the absorption rate of the material to the laser,when the surface heat source power utilization rate:body heat source power utilization rate of 3:7,the most accurate response to the absorption of laser energy of the Invar alloy material,under the numerical simulation,the preliminary determination of a single factor test process parameters range as laser power 1400W-2000W,welding speed 24mm/s-48mm/s;(2)The optimal process parameters for laser stack welding of three-layer thin plates of Invar alloy are welding speed of 36mm/s,laser power of 1800W,shielding gas flow rate of 10L/min and defocusing amount of 0mm;(3)Under the heat source model established in this paper,the experimental results are in high agreement with the simulated results,the error in the value of weld depth and width is within 5%,and the cross-sectional profile is basically fitted,which proves that the validity of the Gaussian composite heat source model established in this paper;(4)In the optimal process parameters,the weld surface is well formed,showing uniform fish scale,weld back without bulge deformation;weld cross-sectional shape of the overall shape of the laser deep fusion welding "nail head" shape characteristics,melt width of 1738.97μm,melt depth of 1597.22μm.weld area is a coarse columnar crystal,a large number of subgrains can be observed in the columnar crystal.The mean hardness of the weld zone is 120.9 HV,which is only 4.6%lower than the parent material,and the hardness of the heat-affected zone is the lowest;the tensile strength is 459.36 MPa,and the elongation can reach 69.67%and the fractures are all in the base metal area;under 100%color penetration,there is no visible spot at the weld,and the permeability meets the industrial testing standard.The research in this paper provides theoretical and technical basis for the application of laser welding of LNG ships Invar alloy three-layer thin plate,and provide a data reference for the later construction of the Invar alloy laser welding process parameters library.