Non-destructive evaluation of mixing and defects of friction stir welded dissimilar AA6061-T6 and AZ31B by X-ray computed tomography

Abstract

Friction stir welding (FSW) is a relatively new manufacturing process employed in the production of parts and components for numerous heavy machinery, including cars planes and spacecrafts. The analysis of welds produced by this method is critical for the safe and successful operation of these devices. Non-destructive testing (NDT) techniques offer a way to evaluate the welds while preserving the specimen. Traditional NDT methods focused on the detection of internal defects and their effect on the weld strength. Ultrasonic, X-ray, Gamma-ray, and other scanning technologies have been employed to analyze these internal defects. The evaluation of material mixing in the thermally and thermally-mechanically affected weld zones (TAZ TMAZ) is a less researched area due to the inability of traditional testing techniques in detecting different materials accurately and in a non-destructive manner. Since having a more homogeneous weld zone will lead to enhanced mechanical properties, having a systematic method to analyze material mixing is highly sought after. In this research, a method for material flow analysis and defect detection by based on computed tomography X-ray (CT X-ray) scans is presented, tested, and corroborated. First dissimilar friction welded AA6061T6-AZ31b welds are produced. The welded samples are then analyzed using the proposed NDT CT X-ray method. Based on the Hounsfield Units values (HU), the CT X-ray scans are segmented using the global Otsu thresholding method into masks for each different material, and 3D renderings are generated. Measurements of materials penetration and transfer are carried out and corroborated using destructive cuts and Energy Dispersive X-ray Spectroscopy (EDX) analysis. The results show that this method can detect internal defects and characterize the material mixing accurately.