Mechanical properties and microstructures of a magnesium alloy gas tungsten arc welded with a cadmium chloride flux

Gas tungsten arc (GTA) welds were prepared on 5-mm thick plates of wrought magnesium AZ31B alloy, using an activated flux. The microstructural characteristics of the weld joint were investigated using optical and scanning microscopy, and the fusion zone microstructure was compared with that of the base metal. The elemental distribution was also investigated by electron probe microanalysis (EPMA). Mechanical properties were determined by standard tensile tests on small-scale specimens. The as-welded fusion zone prepared using a CdCl2 flux exhibited a larger grain size than that prepared without flux; the microstructure consisted of matrix α-Mg, eutectic α-Mg and β-Al12Mg17. The HAZ was observed to be slightly wider for the weld prepared with a CdCl2 flux compared to that prepared without flux; thus the tensile strength was lower for the flux-prepared weld. The fact that neither Cd nor Cl was detected in the weld seam by EPMA indicates that the CdCl2 flux has a small effect on convection in the weld pool.