Evaluation of Friction Stir Spot Welding Process by Laser Ultrasonic Method with Synthetic Aperture Focusing Technique

The application of laser ultrasonic technique is developed for evaluation of friction stir spot welding (FSSW) quality. The features of laser-generated ultrasonic waves in good welding and incomplete fusion area are simulated by finite element method (FEM). The non-contact laser ultrasonic inspection system (LUIS) was established to verify the numerical results. The interaction of laser ultrasound with the welding joint has been investigated. Laser ultrasonic reflected waves in good welding and incomplete fusion area can be distinguished according to some signatures. The shear waves may be more sensitive to incomplete fusion defects than the longitudinal waves in testing the welding joint. The C-scan results can sufficiently evaluate the intrinsic characters of welding area by time-domain synthetic aperture focusing technique (T-SAFT) processing. The research results show that the laser ultrasonics would be an effective method to realize detection of FSSW defects.