Study On Magnetic Field Effect Of Magnesium/Aluminum Magnetic Field Assisted Laser Welding

Magnesium alloys and aluminum alloys are two of the most lightweight non-ferrous metals in the aerospace transportation field,but the physical and chemical properties of the two metals are significantly different,making it difficult to obtain excellent welded joints.In this paper,1.4mm thick AZ31 B magnesium alloy and 1.2mm thick 6061 aluminum alloy were selected as the research object,and the laser lap welding test under the lateral and longitudinal magnetic field assisted magnesium on aluminum was carried out,through high speed camera,micro spectrometer,metallographic microscope and belt.Scanning electron microscopy of EDS probes was used to study the morphology and spectral information of metal vapor/plasma,the weld and molten pool morphology,and the Mg-Al compound distribution in the molten pool,and established a numerical model of the magnesium/aluminium laser welding pool.The mechanism of the external magnetic field to improve the magnesium/aluminum laser welding pool is explored.The research expects to provide experimental basis and theoretical basis for the aerospace transportation magnesium/aluminum dissimilar metal laser welding and the lightening process of the transportation industry.Firstly,the morphology and spectral information of the metal vapor/plasma above the molten pool in the magnesium/aluminum magnetic field assisted laser welding process are studied in this thesis.It is found that when there is no magnetic field,the metal vapor/plasma above the molten pool is dispersed and the brightness is low.In addition to the transverse magnetic field,the density of the metal vapor/plasma above the molten pool becomes larger,the shape is brighter,the metal vapor/plasma particle density increases;and the longitudinal magnetic fiel d is applied,the metal vapor density above the molten pool is also increased,and the color is relatively bright.The metal vapor/plasma density is increased;the applied magnetic field causes an increase in the heat of the weld pool,indicating that the applied magnetic field facilitates the absorption of the laser energy.Secondly,based on the laser lap welding process adjustment,the basic process parameters(laser power 1400 W,welding speed 1500mm/min,defocusing amount 0mm,high purity Ar gas flow rate 15L/min)were obtained;Magnetic field-assisted laser welding experiments show that when the transverse magnetic field is applied,the degree of ablation of the weld becomes larger.After increasing the transverse magnetic field intensity,the molten pool tends to be symmetrical V-shaped straight side,the area of the molten pool increases,and the crack and porosity defects decrease first.Afterwards,the distribution of Mg-Al compounds in the molten pool tends to be uniform;If we apply the longitudinal magnetic field,the degree of ablation of the weld becomes larger.After increasing the longitudinal magnetic field intensity,the molten pool also tends to be a symmetrical V-shaped straight side.The melting width of the molten pool is narrowed,the penetration depth is deepened,and the cracks and pore defects are reduced.However,if the magnetic induction strenth becomes too large,the defects are increased,and the distribution of the Mg-Al compound in the molten pool tends to be uniform.These phenomena indicate that the magnetic field can stir the molten pool;at the same intensity,the transverse magnetic field promot es the absorption of laser energy by the metal material better than the longitudinal magnetic field,while the longitudinal magnetic field agitates the molten pool better than the transverse magnetic field.Finally,the thermo-flow-metallurgical numerical model of magnetic fieldassisted laser welding is established.The welding process is simulated and found that the temperature field gradient of the molten pool is greatly reduced after the addition of magnetic field,which promotes the effective transfer of heat in the molten pool.The energy distribution of the molten pool is more uniform and the molten pool area is enlarged.Compared with the case where no magnetic field is added,the flow velocity of the molten pool is greatly increased.The metal in th e molten pool undergoes a rotational motion under the agitation effect of the Lorentz force,and a vortex is generated,and the vortex center is the center of the molten pool.The simulation results confirm the promotion of the magnetic energy absorbed by the molten pool and the stirring effect of the magnetic field on the molten pool..