Study On Arc Morphology And Weld Microstructure And Properties Of Al-Cu Aluminum Alloy Magnetically Controlled MIG Welding

With the development of aerospace,ocean engineering and military industry,the application rate of Al-Cu series aluminum alloy is increasing year by year because of its light weight,good electrical conductivity and thermal property.During the welding process of this kind of aluminum alloy,the physical and chemical properties of Cu element and Al element in the alloy are quite different,so there is the possibility of porosity and hot crack.In order to solve related problems,this subject realizes the magnetic field assisted MIG welding process by designing a magnetic field generating device.The excitation current and excitation frequency of the magnetic field generator are respectively adjustable,and then the two excitation parameters are orthogonally matched to evaluate the weld morphology,metallographic structure and mechanical properties under different excitation parameters.Finally,the best excitation parameters suitable for Al-Cu series aluminum alloys are obtained.In order to further analyze the effect of magnetic field,a feasible magnetic field generator was designed and manufactured by simulation method.Through the device,the arc area,molten pool area and heat affected zone can be effectively covered.In the above regions,the magnetic field strength is more than 10 m T,and the magnetic field strength can be improved by increasing the excitation current.During the experiment,the arc behavior under the action of magnetic field was observed by high-speed camera system.It was found that the arc shape changed obviously under the action of magnetic field,and the arc shape gradually appeared bell cover shape under the action of magnetic field.The change of excitation current will affect the degree of bell cover shape,that is,with the increase of excitation current,the phenomenon of middle arc contraction is more obvious.In the excitation frequency range of this experiment,with the increase of excitation frequency,arc rotation causes arc expansion.Under the appropriate excitation parameters,the weld surface forming quality is obviously improved,and the 5 A-70 Hz excitation parameters have the best surface forming quality.Under the magnetic field,the grain size in the weld zone is more refined,which is66.57% higher than that without magnetic field.The results show that the equiaxed grain zone with non-uniform size appears on the side of the fusion line,and columnar grains are formed at the edge of the equiaxed zone due to temperature gradient.In the central region of the weld,the fluidity of the weld pool is increased due to the magnetic field,and the finer equiaxed grain structure is obtained.Under the action of magnetic field,the mechanical properties of weld are improved in different degrees.Under the influence of magnetic field,hydrogen clusters gather and grow between grains.However,improper excitation parameters will increase the resistance of bubbles to escape,thus forming large-scale continuous bubbles near the weld surface,which will affect the mechanical properties of the weld.Under the 5 A-70 Hz excitation parameters,the bubbles can escape smoothly,and no hydrogen pores can be seen in the SEM image of weld section.