Non-destructive Evaluation of Friction Stir Welded Joints by X-ray Radiography and Infrared Thermography

Digital X-ray radiography and infrared thermography techniques are used for evaluation of the quality of the friction stir welded aluminum butt joints and aluminum-zinc coated steel dissimilar lap joints. Digital frame integration and gradient operation based image processing techniques are used on the radiography images which ensured 48% increase in the signal-to-noise ratio. The effects of various welding parameters like tool rotation; travel speed etc. on the quality of the weld are studied. A sub-surface tunnel defect along the weld line of a butt-joint is detected using infrared thermography technique and it is observed that the rate of temperature decay is lower for the defect regions. Using lock-in thermography technique, the optimum frequency is determined and the defect depth is quantified at this frequency. Improved visualization and contrast sensitivity are achieved using adaptive single plateau based histogram equalization on the acquired infrared images.