Characterization of Microstructure, Weld Heat Input, and Mechanical Properties of Mg-Al-Zn Alloy GTA Weldments

The present study investigated the influence of welding speed on the microstructure, hardness, and tensile properties of the AZ31 Mg alloy gas tungsten arc (GTA) welds that were prepared using alternating current (AC). A microstructural examination of the weld metal and base metal was performed using stereo, optical, and scanning electron microscopy (HR-SEM and EDS) techniques. The microstructure of all fusion zones consists of two parts: a columnar zone, adjacent to the fusion boundary, and equiaxed grains, in the centre of the weld fusion zone. It is shown that the average width of the equiaxed zone present at the centre of the fusion zone increases with increasing welding speed. Metallographic examination shows that the highest welding speed (5 mm/s) results in the smallest average grain size. The welds prepared with high welding speed exhibit an increase in strength, hardness, and ductility compared with other welding speeds, which is attributed to low heat input.