Acoustic Emission Technique for Detection and Identification of Defects in Friction Stir Welded AA6061-T6 Al Alloy Joint

Fusion welding of AA6061-T6 repeatedly results in flaws, including lack of fusion, incomplete penetration, cracking, and oxidation. To avoid or control these defects, solid-state welding, such as Friction Stir Welding (FSW), is a reliable alternative for creating high-strength joints and is widely used in automotive, aerospace, electrical, and marine applications. This research investigates the real-time monitoring of FSW in similar AA6061-T6 joints using the Acoustic emission technique for defect detection during welding. Welding has been done defect-free, as well as with piping defects and pinhole defects. A defect-free joint has a maximum tensile strength of 295 MPa, and failure occurred in a thermomechanically affected zone, due to precipitate dissolution and grain coarsening. Microstructural examination confirms that finer grains in the Stir zone of defect-free joints have a maximum hardness of 110 HV. Additionally, it analyzes and deliberates the Acoustic emission parameters (RMS, Hits, Amplitudes, and Counts), Acoustic emission Fast Fourier Transform, and Acoustic emission waveform variations under various defect conditions. Acoustic emission signal patterns clearly distinguish defect-free weld joints from those with piping defects and pinhole defects, which exhibit prominent variations due to larger defect areas. The findings confirm that Acoustic emission monitoring is consistent in detecting and analyzing welding defects.