Gas-tungsten arc welding of AZ91 magnesium alloy

The gas-tungsten arc (GTA) welding behaviors of the commercial AZ91 magnesium alloy were examined in terms of process efficiencies and microstructure characteristics. This study focused on the effects of GTA welding process parameters (like welding current in the range of 100/300 A and welding speed in the range of 3.33/13.33 mm/s) on energy absorption by the substrate material. The dependences of arc and welding efficiency on the used process parameters were presented. The measurements revealed that the arc efficiency values ranged from 0.63 to 0.88. Melting efficiency was found to rise with both increasing welding current and speed. The analyses revealed a strong influence of the GTA welding process on the width and depth of the fusion zone and also on the refinement of the microstructure in the fusion zone. The results of dendrite arm size (DAS) measurements were presented. Additionally, the presence of a partially melted zone (PMZ) was disclosed.

► For the commercial AZ91 magnesium alloy, the arc efficiency values ranged between 0.63 (with 100 A current and 3.33 mm/s welding speed) and 0.88 (with 300 A current and 3.33 welding speed) and rose with an increase in welding current and fell with an increase in welding speed.
► Melting efficiency rises with both an increased welding current and speed to the maximum value of 0.41 using a welding current of 300 A and speed of 13.33 mm/s.
► The GTA welding process strongly influenced the width and depth of the fusion zone and also the refinement of the microstructure in the fusion zone. The DAS of the remelted material dropped with an increase in welding speed.
► Due to the low-melting nature of the eutectic in Mg–Al type alloys, the presence of a partially melted zone (PMZ) was formed in a commercial AZ91 magnesium alloy, GTA welded using all the process parameters presented.