Abstract: A three-dimensional friction stir welding(FSW) process model is developed based on fluid mechanics. The material transport in the welding process is regarded as a laminar, viscous and non-Newtonian liquid flows past a rotating pin. A criterion to divide the weld zone is given on the basis of cooperation of velocity field and viscosity field. That is, the h0-easy-flow-zone existed near the tool pin is corresponded to the weld nugget zone, the area between theh0-easy-flow-zone andh1-viscosity-band is corresponding to TMAZ. Results of the simulation show that the material in the middle part of the weld flows vertically. In the retreating side the material is pushed up and in the advancing side the material is pushed down. Material flow visualization experiments of marker insert technology are used to validate the simulated results. The experimental images can agree well with the simulated results. Under higher welding speeds, material separated motion can be seen in the shoulder-pin transition part, and an actual welding defect of void is observed at the same position in the weld seam.

Key words: Al 2014 alloy, Flow Numerical simulation, Friction stir welding