Investigation of void formation in friction stir welding of 7N01 aluminum alloy

Friction Stir Welding (FSW) is a solid state joining process that is widely used to produce high integrity aluminum weldments for a variety of industries. While extensive work has been conducted to understand flow behavior, much less research has been performed to identify how void defects form and how to predict them. In the present study, the relationship between rotation speed, plasticized region, and defect formation was investigated. To analyze how tunneling and cavity type void defects form during FSW, a 3-D Computational fluid dynamics (CFD) model based on the Fluent software code was used to simulate butt welding. The CFD model was validated using temperature measurements and marker materials from FSW welds made on 12 mm thick 7N01 aluminum alloy plate. Analysis of the simulation results showed that the formation of tunneling defects at lower rotation speeds correlated to a large variation in the size of the plasticized region over the plate thickness. At higher rotation speeds, analysis of material flowlines indicated an imbalance in rotational and longitudinal flow around the pin which resulted in a cavity type defect. It is considered that the results can be used to compare different weld schedules and be used to assess the likelihood of void formation in an actual weld using a CFD model.