Inspection of defects in friction stir welded Al-7075 T6 alloy

In this work, the evaluation of tunnel defects in Al-7075 T6 sheets processed by friction stir welding (FSW) is explored using computed tomography (CT) and the finite element method (FEM). The effect of axial force and temperature generated during the FSW was assessed using four rotary speeds (1600, 1700, 1800 and 1900 rpm), each at two different welding speeds (15 and 30 mm/min). These joints were CT-scanned, reconstructing the voxels from the X-Ray images. A voxel size of 46 m, a spot size of 59 m and a magnification of 4.35 using a Cu filter of 0.5 mm were selected. The 3D images of the welds showed the forms, places and levels of the detected defects. The tunnel defects were found at 2 mm from the bottom edge of the weld plates, and the tendency for the defects formation was reduced at 1900 rpm based on CT scans. The numerical results of FSW revealed that with a higher rotational speed, the generated heat and strain were increased, while the stress decreased for higher welding speeds. The coupling of CT and numerical results provide an in-depth understanding of material flow and defect formation during friction process.