Effects of activating fluxes on metal inert gas welding of AZ31B magnesium alloy

摘要

In this paper, the activating fluxes including ZnCl2, CdCl2, TiO2 and MnO2, have been successfully applied to the metal inert gas welding of AZ31B magnesium alloy. Moreover, the full-penetration butt weld prepared with ZnCl2 flux in 6-mm-thick plates with a single-pass square groove is obtained. Meanwhile, the effects of activating fluxes on weld bead morphology, arc profile and voltage are investigated. The mechanisms in increasing weld penetration for activating fluxes are discussed. The microstructure, mechanical properties and fracture characteristic of the full-penetration butt joint with ZnCl2 flux are also evaluated. The results indicate that all fluxes can augment the weld penetration and depth-width ratio of the metal inert gas welded magnesium alloy. The ZnCl2 and CdCl2 fluxes can constrict the welding arc and increase the arc voltage. However, the effects of TiO2 and MnO2 fluxes on arc profile and voltage are slight. The main mechanism of ZnCl2 and CdCl2 fluxes increasing weld penetration is the arc constriction and the increase of arc voltage is also beneficial to the improvement of penetration. In addition, the fusion zone of the full-penetration butt weld produced by ZnCl2 flux displays more uniform equal axis crystals and more precipitates compared with base metal. The ultimate tensile strength of the butt joint is 92.4% of base metal and the elongation comes up to 12%. The SEM fractograph demonstrates that the ZnCl2 flux obviously influences the fracture pattern of the butt joint.