TIG and laser-TIG hybrid filler wire welding of casting and wrought dissimilar magnesium alloy

Cast magnesium alloy AZ80 and wrought magnesium alloy AZ31B subjected to tungsten inert gas (TIG) filler wire welding and laser-TIG hybrid filler wire welding were investigated. The welding formation, microstructure, and mechanical properties of the two joints were analyzed. Results showed that although good welding formation and good tensile strength can be achieved both in two welding methods, hybrid welding possessed wider parameter than TIG welding, which made it more flexible and reliable in industry application. The weld beads of the two joints both had irregular anchor shapes, and both joints had a sharp angle region on the AZ31B sides. The microstructure of the joints was composed of α-Mg phases and β-Mg17Al12 phases, and α + β divorced eutectic phases were found in the fusion zone (FZ), AZ80 base metal (BM) and AZ80 partially melted zone (PMZ). The FZ was observed as small equiaxed dendrites and an evident PMZ, whose microstructure was a reticular α + β eutectic phase belt and some nongrown α-Mg phases, was observed on the AZ80 sides in both joints. The eutectic phases were tinier and more dispersed in hybrid welding than in TIG welding. The hardness value of hybrid welding was higher than TIG welding, and the PMZ was the hardened zone in both joints. The tensile test showed that the ultimate tensile strength (UTS) of both joints were over 155 MPa, and the joints fracture at the AZ80 base metal. The increased hardness and high tensile strength of each joint were attributed to the PMZ microstructure. Moreover, the factors that contributed to the special welding formation, sensitive welding parameters, and changes in PMZ microstructures were discussed.