Research On P-GMAW Welding Technology Of 5083 Aluminum Alloy With Axial Magnetic Field

5083 aluminum alloy is widely used in the manufacture of LNG carriers.The welding method used is Pulsed Gas Metal Arc Welding(P-GMAW).A considerable number of welding positions are horizontal welding,which is difficult to weld.Due to the small surface tension and low viscosity of aluminum alloys,under the action of gravity,the problem of squatting in the molten pool often occurs,resulting in welding defects such as overlap and unfusion.Studies have shown that it is possible to counteract the effect of gravity by applying an external axial magnetic field on the molten pool to produce a Lorentz force opposite to the direction of gravity.Since electric current flows through the arc,the droplets,and the molten pool,the introduction of the axial magnetic field is bound to affect the arc motion,the droplet transfer,and the molten pool flow.This paper constructs a GMAW welding platform with an applied axial magnetic field,including automatic welding system,magnetic generating device,high-speed photography system and electrical signal acquisition system.Aiming at the P-GMAW process of 5083 aluminum alloy,the effects of external axial magnetic field on arc shape,droplet transfer,molten pool flow and weld formation were studied,and its mechanism was analyzed.The research results of this paper have important guiding significance for further understanding the influence of external axial magnetic field on the P-GMAW process of 5083 aluminum alloy and its mechanism.The results show that after the application of the axial magnetic field,the lower part of the arc expands and rotates with the wire as the axis.As the magnetic induction intensity increases,the arc length decreases first and then increases.When the direction of the magnetic field changes,the shape of the arc does not change much,but the direction of rotation of the arc changes.When the welding current is small,the arc length becomes shorter after the external magnetic field is applied.According to the analysis,after the application of the axial magnetic field,the charged particles moving in the arc are subjected to the Lorentz force perpendicular to the moving direction.The trajectory of the charged particles from the welding wire to the molten pool changes from the original straight line to the spiral shape,which is macroscopically expressed as the arc rotates.By analyzing the droplet transfer photos taken by high-speed photography,it is found that the shape of the ER5183 welding wire P-GMAW droplets is not a regular spherical shape,and the surface of the droplets is uneven,which is mainly due to the evaporation of magnesium in the welding wire.When a small diameter wire is used or the welding current is reduced,the shape of the droplet becomes relatively regular.After the application of the magnetic field,the shape of the droplet becomes flat and the falling speed becomes faster.In order to better study the influence of magnetic field on the droplets,the experiment was carried out with aluminum-silicon alloy welding wire ER4043.The droplets of the ER4043 wire are regular spheres.The introduction of the magnetic field causes the droplet to rotate and flatten,and the degree of flattening increases as the magnetic induction intensity increases.According to the analysis,the magnetic field acts on the current flowing through the droplet to produce a tangential Lorentz force,which causes the droplet to rotate and flatten.Under the action of the magnetic field,the droplets become flat and the falling speed becomes faster,which increases the impact force of the droplets on the molten pool,but does not cause the weld to be offset.In the aspect of weld formation,the influence of the applied axial magnetic field on the formation of the flat weld is first studied.In the case of flat welding,the direction of the weld offset is perpendicular to the direction of gravity,which can eliminate the effect of gravity and study the effect of the applied axial magnetic field on the weld offset.Analysis of the mechanism of action and results obtained under flat welding can be used to guide the direction of the magnetic field during horizontal welding.The results show that after the application of the axial magnetic field,the molten metal in the molten pool flows more to one side,and the weld has a vertical deviation from the welding direction.When the direction of the magnetic field or the direction of the weld changes,the direction of the weld offset changes.As the magnetic induction intensity increases,the degree of weld offset gradually increases until the weld bead is broken and the surface is uneven.Under the action of an external magnetic field,the weld offset increases as the welding speed decreases.The use of an external magnetic field for horizontal welding can suppress the squat of the molten pool.According to the analysis,the external magnetic field causes the molten pool to be asymmetrically stirred,and the weld is offset during the flat welding.The horizontal welding can offset the gravity of the molten pool and inhibit the squatting of the molten pool.