Partially melted zone microstructural characterization from gas tungsten-arc bead on plate welds of magnesium AZ91 alloy

The partially melted zone (PMZ) found in gas tungsten-arc (GTA) welding of Mg-AZ91 alloy was studied. The microstructure, aspect ratio and defect formation was investigated by optical and scanning electron microscopy. The distribution of the alloying elements was measured by using energy dispersive X-ray spectroscopy (EDS) and chemical analysis. Due to the low heat capacity and good thermal conductivity of the Mg alloys, PMZ was created adjacent to the fusion line. In the PMZ, most of the interdendritic regions as well as the grain boundaries were fully melted and acted as channels to transport the melt metal from the weld pool to the root face, forming the melted and resolidified layer.