Weld nugget formation of friction stir welded AZ31 magnesium alloy and its affecting factors

The main character of friction stirred weld is the formation of the weld nugget. The shape and size of the weld nugget have great effects on the joint mechanical properties. AZ31 magnesium alloy used as base metal and the effects of welding parameters including welding pressure, welding speed and probe tilt angle on the weld nugget formation were studied and a simple model was built to explain the weld nugget formation process. The results showed that the welding pressure and the probe tilt angle are the most important factors on weld nugget formation and the formation of superplastic material depends on the welding pressure. The shape of the weld nugget was affected by the material flow pattern, and the flow movement was caused by the probe and the welding speed, then affecting the weld nugget formation. A good understanding of the weld nugget formation can be used to choose reasonable welding parameters.