Defects formation procedure and mathematic model for defect free friction stir welding of magnesium alloy

Though friction stir welding is thought to be one of idea methods for joining nonferrous metals and has gained some perfect results on certain materials, defects could not be completely avoided for some metals especially using improper welding parameters. The pore and insufficient penetration at the bottom of the weld are easy to occur when the welding speed is too fast or the welding pressure is too small. Obvious materials flow characterization was left around the pore and can be used to study the whole superplastic material flow patterns during FSW. AZ31 magnesium alloy was friction stir welded at different welding parameters to get the best conditions for defect-free weld. The relationship between materials flow and defects was firstly built in this paper. A model of the weld formation depending on the welding parameters was brought forward, and gives reasonable advice for choosing right parameters to avoid defects.