Non-destructive Testing of Porosity in Laser Welded Aluminium Alloy Plates: Laser Ultrasound and Frequency-Bandwidth Analysis

Embedded welding defects, such as porosities and cracks, are generally formed during aluminium laser welding. It is challenging to test these defects with current non-destructive evaluation (NDE) methods. This work features the creation of defects and their study with the help of NDE methods. The chosen method should be able to detect porosities in lap-welded sheets of 5754 aluminium alloys. The welding process is described and the samples were first characterised with X-ray techniques to choose those containing defects of various sizes and densities. Secondly, these welds were tested with the Laser Ultrasonic Technique (LUT). The first results show that LUT gives defect signatures. Based on raw measurements only, our results show that it is difficult to give any precise description of the defects' size or position. To aid in the interpretation of the results, a frequency-bandwidth analysis has been performed because of the broadband nature of laser ultrasonic signals.