The Research Of Arc Characteristic And Weld Bead Microstructure And Property Of Aluminum Alloy Magnetic Control MIG Welding

In the development of modern manufacturing industry of pursuing light weight,Al-Mg aluminum alloy is used more and more widely.But due to the bad formation,crystal structure bulky and high porosity,the use of MIG welding in the joining of aluminum alloy is still highly restricted.In this work,the alternative longitudinal magnetic field was introduced to joining of 5083 aluminum alloy and the influence of excitation current and excitation frequency on arc shape,droplet transition and molten pool was investigated.The influence regulation of the magnetic field parameters on the welding arc,droplet transition crystal structure,mechanical properties and porosity was analyzed by using of high-speed camera,metallographic analysis,mechanical property test and X-ray nondestructive flaw detection and the mechanism of working was also explored.The arc movement and the droplet transition were observed by using of high-speed camera and electrical signal dynamic analysis system.Meanwhile the mechanism of arc movement was analyzed by building mechanical model of particles in the arc space.The experiment comes to conclusions: the arc shape is similar to cone without magnetic field.But when alternative longitudinal magnetic field is applied,with the increase of excitation current and excitation frequency,the welding arc becomes rotation.With the increase of excitation current,the degree of arc rotation is strengthened and the arc shape is show that the first expansion and then contraction.Especially,when the excitation current is 2A and excitation frequency is 45 Hz,the welding arc is shown as the central symmetrical distribution with the wire as the axis.The arc shape turn to bell shape from the cone without the magnetic field.With the increase of magnetic field parameters,the droplet turns to the ellipsoidal from the globular without the magnetic field.The droplet transition frequency first increases and then decreases.When the excitation current is 2A,the maximum droplet transition frequency is up to 5.8ms per drop.When the magnetic field parameters increase in a certain range,in macroscopic morphology,the weld surface fish-scale patterns become denser.The weld width first increases and then decreases.But due to the increase of excitation current,weld penetration first decreases and then increases.While the welding process is steady,weld penetration is less affected by the excitation frequency.In microstructure,the transformation of crystal structure from columnar crystal to equiaxed crystal is promoted by introducing the magnetic field.Meanwhile,the grain size becomes smaller.Especially,when the excitation current is 2A and excitation frequency is 45 Hz,the weld bead microstructure is small.At the same time,compared with that without external magnetic field,the tensile strength of the welded joint is increased by 34.7MPa,the elongation is increased by 5.86% and the maximum hardness is increased by 11 HV.With the introduction of the external magnetic field,the number of holes on the unit length of weld bead is decreased obviously.The results show that the magnetic field parameters have a significant influence on the porosity of the weld bead.When the excitation current is 2A and excitation frequency is 45 Hz,the number of holes in the weld bead is changed from 8 without magnetic field to 2.The porosity of weld bead are reduced.