Study On MIG Welding With Activating Flux For Magnesium Alloy

In the present study, the MIG welding of AZ31B and AZ61magnesium alloy plates with activating flux is studied and the addition of activating flux increase the penetration depth, improve the metal transfer and reduce the spatter during MIG welding of magnesium alloy. The high-speed camera is used to observe and investigate the welding arc profile and the metal transfer behavior during welding. After welding, the optical microscope, the scanning electron microscope, the electron microprobe, the tensile testing machine and the microhardness tester are employed to analyse the microstructure and mechanical property of the joints. The main results are as follows.1. For the TiO2, MnO2, ZnCl2, and CdCl2fluxes, all can augment the penetration capability and the depth-width ratio of the MIG welding of magnesium alloy. Moreover, because ZnCl2and CdCl2fluxes can constrict the welding arc intensely and increase the arc voltage obviously during welding, the main mechanisms in increasing penetration depth for them are the constriction of welding arc and the increment of arc voltage will be also one of the reasons for improving the penetration depth. However, because the effects of TiO2and MnO2fluxes on the arc and arc voltage are slight and the two fluxes contain surface active oxygen element, the mechanisms of increasing the penetration depth for them should be the reversal of the Marangoni convection.2. Compared with traditional MIG welding, the KC1flux can increase the welding current and the arc conductivity, and reduce the droplet size and the period of metal transfer, accordingly promoting the droplet transfer and decreasing the spatter loss during MIG welding. In addition, the main reason for forming the stable metal transfer and fewer spatters on KC1flux lies in the enhanced electromagnetic force resulted from the increment of welding current in MIG welding of magnesium alloy. The increased welding current caused by the augment of arc conductivity.3. For MIG welding of magnesium alloy with KCl or CaCl2flux, the arc conductivity is controlled together by the metallic atoms (K atom or Ca atom) and the chlorine atoms involved in the two fluxes. Moreover, the eventual result will depend on the strengths of the influences of both metal and chlorine atoms on the arc conductivity, in other word on the principal factor between the two kinds of atoms, owing to that the metallic atoms can augment the conductivity, and yet the chlorine atoms can deteriorate it.4. In MIG welding of magnesium alloy with the compound activating flux, it can not only increase the penetration depth to180.2%of that of single MIG welding and increase the depth-width ratio to170.66%of that of single MIG welding, but also improve the weld appearance. Moreover, compared to single MIG welding of magnesium alloy, the compound activating flux can also reduce the droplet size and the period of metal transfer, and then promote the metal transfer and decrease the spatters during MIG welding. Meanwhile, the tensile strengthe of the weld bead with the compound activating flux is261MPa, up to92.88%of base metal, and the elongation of the weld bead is11.23%, reaching to70.2%of base metal.