Study On Laser-MIG Hybrid Welding Technology Assisted By An External Longitudinal Magnetic Field

It is widely accepted and actively promoted of the research of using external magnetic field to control the welding joint shape and performance during the welding process by scholars and engineers.And these research show that the magnetic field can stir the molten pool effectively,reduce the element segregation,and optimize the microstructure and mechanical property of joint,leading a high quality welding joint.However,the research focuses on arc-magnetic field hybrid welding and laser-magnetic field hybrid welding,and there is no research reported about laser-MIG-magnetic field hybrid welding.Therefore,this paper studies the effect of magnetic induction intensity on arc/droplet transfer dynamics behavior,macro-morphology and microstructure of joint,and mechanical properties on the build experimental platform of laser-MIG hybrid welding using external longitudinal magnetic field.Dynamic behavior of arc/droplet transfer is analyzed by means of high-speed photography.It is found that the arc rotates at a high speed and the bottom diameter increases under the magnetic field,which makes the stiffness and stableness of arc are strengthened.And the direction of arc changes from the direction of keyhole to the axial direction of filler wire,and finally deviates the filler wire gradually.When the droplet transfer mode is short-circuiting transfer,the electromagnetic force of short-circuiting is increased by magnetic field,which increases the transfer frequency and decreases the diameter of droplet.And the direction of droplet is parallel with filler wire under 8mT and12mT,while there is a bevel forming in the telos of filler wire,where the droplet forms and grows.When the droplet transfer mode is projected transfer,the liquid metal beam is longer under magnetic field.And the transfer is more stable and uniform under 8mT,while the liquid metal beam rotates under 12mT and 16mT when the centrifugal force becomes the main driving force of droplet transfer.The influence of magnetic induction intensity on macro-morphology and microstructure is studied and the mechanism is revealed.The welding width of non-penetrating joint increases with the magnetic induction intensity increasing,while the reinforcement decreases.The macro-morphology changes from pin-fin shape to mushroom shape.Penetrable joint width also increases with magnetic induction intensity increasing.And the crater is restrained.The crystal homogeneity of non-penetrating and penetrable joint is enhanced under magnetic field.The microstructure of welding joint changes from skeletion+lathy to only skeletion,and the grains are refined,which decreases with the depth of welding joint increasing.The molten pool area largens and the temperature of high temperature region and staying time increase influenced by magnetic field,which leads to elongated ferrite separating out in HAZ.The effect of magnetic field on welding joint mechanical properties is valued.And it is found that the increasing of magnetic induction intensity makes a more stable micro-hardness,which indicates that a more crystal homogeneity is obtained.And the tensile strength is improved under magnetic field,and the max percent of increasing is 4.6%at 16mT.The reason is that porosity quantity and size is reduced,macro-morphology is optimized and microstructure is homogeneity under magnetic field.The welding joint open circuit potential E_CORR is increasing which indicates the corrosion resistance enhancing.