Influence of the FSW clamping force on the final distortion and residual stress field

Friction stir welding (FSW) is a solid state process, leading to joints with good mechanical performance. Low residual stresses and distortions are generally mentioned as further advantages, leading to the current high interest of the aeronautical industry in this process.In order to achieve these beneficial properties, the welding process requires clamping of the parts to be welded. To the authors knowledge clamping forces in FSW have not been studied in detail yet, neither their influence on residual stress and distortion.In the present work the clamping forces, both initially applied and their evolution during the welding process, were studied. Furthermore the influence of different clamping forces on the distortion and residual stress of the welded plates was analysed. The joints were subjected to mechanical testing and microstructural analysis in order to guarantee defect free joints in all cases and in order to be able to detect influences of the clamping process on joint performance.It was found that higher clamping forces lead to lower distortion and a more uniform residual stress distribution through the thickness. Higher clamping forces also lead to a lower defect probability through the creation of gaps between the plate halves.

► Lower FSW clamping forces lead to lower residual stress and higher distortion.
► Higher clamping forces produce more uniform through the thickness residual stress.
► Higher clamping forces reduce the overall distortion.
► Higher clamping forces lead to lower scatter of the tensile properties.