Study On Technology And Microstructure And Mechanical Properties Of Laser-MIG High-speed Hybrid Welded Of Ship Superstructure Sheet

Thin plate structure is widely used in ship superstructure manufacturing industry because of its small weight.When traditional arc welding?MIG,MAG?is used for thin plate welding,the welding deformation is often caused by the large heat input in the welding process.Laser-MIG hybrid welding is a new high energy beam welding method,which can improve welding efficiency and reduce welding deformation.In this paper,a Laser-MIG hybrid welding process test was carried out on butt joint and T-joint of 6mm Q345E steel to study the influence of different welding process parameters on weld formation,the welding speed range of butt joint and T-joint in different match gaps is explored,and the form and frequency of droplet transition at different welding speeds are described.The optimal welding parameters were used to weld the butt joint and T-joint,and the microstructure,mechanical properties and angular deformation of T-joint under different heat input were studied.By means of high speed photography technology,the specific droplet transition forms and transition frequencies under different welding parameters were studied.Under the welding process parameter window of laser power 4⁵.8kW,welding current 200³20A,D_LA 2mm and defocusing distance-5mm,when the welding speed changes within the range of 1.5⁴.2m/min,the droplet transition form is stable short circuit transition,shoot droplet-short circuit-jet flow and single jet flow transition,the transition process is relatively stable,and the weld formation is well formed.When the welding speed is4.5m/min,the droplet directionality changes,and the droplet transition form is a dislocated jet-short circuit alternating change transition form,and a large number of spatter and hump defects appear on the weld surface.The optimized welding process parameters were used to conduct the Laser-MIG hybrid high-speed welding process test of butt joint and T-joint.Under the premise of ensuring the welding quality,the maximum welding speed of butt joint was up to 4.2m/min,and the maximum welding speed of T-joint was up to 3.9m/min.With the increase of match gaps,the maximum welding speed decreases gradually.For the butt joint,when the match gaps of the workpiece changes from 0.6mm to 1.0mm,the maximum welding speed decreases from 2.1m/min to 1.8m/min.For T-joints,when the match gaps changes from0.4mm to 0.8mm,the maximum welding speed decreases from 2.4m/min to 2.1m/min.The experiment of Laser-MIG hybrid high-speed welding was carried out with the optimized welding process parameters to study the angular deformation and mechanical properties under different heat input.When the welding heat input changes in the range of3.5².2kJ/cm,the angular deformation of T-joint decreases with the decrease of welding heat input.When the welding heat input is 2.2 kJ/cm,the angular deformation is only 0.9°,compared with 3.5 kJ/cm welding heat input,the angular deformation reduced 54%.With the decrease of welding heat input,the microstructure of weld changed from block ferrite+lower bainite to lath martensite.The microstructure of super heating zone is composed of a large number of lath martensite.When the welding heat input is 2.1kJ/cm,the maximum hardness of the welded joint appears in the heat affected zone;the tensile fracture positions of the welded joints are all in the base metal.