Study of GTA-Welded Joints of ZW61 Magnesium Alloy - Effect of Welding Current on the Microstructure and Mechanical Properties

An attempt has been made to weld ZW61 magnesium alloy extruded plates by gas tungsten arc welding (GTAW). In this paper, the zone with the largest average grain size in the welded joint was the fusion zone (FZ) rather than the heat-affected zone (HAZ). The grains of the FZ were nearly equiaxed, and their average size increased gradually with the increase of welding current. Simultaneously, the mechanical properties of the joints decreased with the increase of welding current under the set conditions of this experiment. The optimum mechanical properties of the joints were obtained at a welding current of 100 A. Their ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) were 230 MPa,103 MPa, and 19.2%, respectively, while the joint efficiency(sigma b/ sigma b BM ) was only 77.7%. The fracture locations of all the joints were found in the FZ. Excessive grain size was one of the significant factors contributing to the weakness of this zone. In addition, the semicontinuous second phase on the grain boundary induced high-stress concentrations, contributing to the fracture of the welded joint. The tensile properties of the joints can be improved by limiting heat input.