Numerical modeling for the mechanism of shoulder and pin features affecting thermal and material flow behavior in friction stir welding

A three-dimensional transient computational fluid dynamics model is developed to analyze the influence of rotational/non-rotational shoulder and pin characteristics on the thermal and material flow behavior in friction stir welded (FSW) aluminum alloy joints. Four tool designs with rotational/non-rotational shoulder and the pin with/without triple facets are considered. The heat cycle of the rotational and non-rotational shoulder friction stir welded joint (RS-FSW and NRS-FSW) is simulated and experimentally verified, and the welding temperature fields are analyzed. The welding peak temperature of the RS-FSWed joint is the highest, and the non-rotational shoulder significantly reduces the welding peak temperature and the range of the heat-affected zone (HAZ). The rotational shoulder promotes material flow and enhances flow velocity, whereas the non-rotational shoulder reduces both. An increase in the triple facets on the pin facilitates the material flow during NRS-FSW. Viscosity is a physical quantity associated with the welding temperature and strain rate, which is affected by the tool characteristics. The deformation zone caused by the tool is related to the viscosity of the material, the closer the tool, the lower the viscosity of the material. The viscosity of the material gradually increases with an increase in the distance from the tool surface.