Interaction of guided waves with friction stir welds of similar and dissimilar materials -

Abstract

Friction Stir Welding (FSW) is a modern solid-state welding technique invented in 1991 at the Welding Institute of Cambridge. It is becoming popular and efficiently used in many applications including automotive, marine, railway and aircraft industries. In addition to defects such as pin holes, voids, and tunnels that may arise from inappropriate selection of weld parameters. The FSW process by itself involves excessive stirring, thermo-mechanical deformation, and changes in grain orientation. Guided waves are ultrasonic elastic waves which have the ability to travel over long distances. Their ability to propagate in complex structures and in both metallic and non-metallic materials, has drawn the attention of many researchers to explore the potential of their use in detecting surface and internal flaws. Defect-inspection in dissimilar friction stir welded joints is associated with several challenges related to the difference in the attenuation behavior between the two mediums. The purpose of this work is to scrutinize the interaction behavior of guided waves with friction stir welded line of similar and dissimilar materials including aluminum and magnesium alloys. The effect of the excessive plastic deformation within the weld line, and the rolling and extrusion directions of the base metals on the wave behavior were investigated. The frequency-wavenumber filtering technique of the data extracted from the laser Doppler vibrometer (LDV) test was used to filter out the reflected wave from the incident and transmitted waves within the three plates. Reflection was observed at the weld zone of the defect-free AA6061-AZ31B FSW plate. On the other hand reflection was not detected at the weld zone of AA7020-AA7020 and AA6060-AA7020 FSW plates. Guided waves propagation highly depends on the elastic properties of the medium, therefore these properties across the three friction stir welded zones were characterized using the nano-indentation (load-unload curves). The results showed constant elastic properties across the