Influence of stirring head structure on the defect formation mechanism in friction stir welding

The friction stir welding stirring head structure and welding process parameters lead to different welding heat inputs and material flow behaviors that result in different types of weld defects. This study simulated friction stir welding of A7N01 material using the Deform software. The model was verified by comparing with measured temperatures and observed defects in welding tests. The model was then used to investigate the influence of three kinds of stirring heads on the weld defect formation. The material particle tangential filling speeds varied with depth for different stiring heads. The circular stirring head mostly created tunnel-type and furrow-type defects, while the plane stirring heads mostly caused half-tunnel-and-half-furrow-type defects. Different process parameters for the same stirring head resulted in different types of defects in the advancing side of the weld. A two-dimensional process parameter selection window was then developed to select conditions that would prevent typical welding defects for each stirring head. The process parameter range is wider for the plane stirring head than for the circular stirring head for friction stir welding.