TWI Industrial Member Report Summary 908/2008
By D S Caravaca, C R Bird, K A Beamish and S J Maddox
Background
Friction stir welding (FSW) of aluminium alloys is now an established joining technique and there is increasing application to joining of critical components and structures. Much emphasis has been placed on optimising tool design and process parameters to ensure joint quality but flaws may still be created in the production environment if the limits of the process window are exceeded. There is a requirement to understand the type of flaws that may be generated, and their causes, when welding conditions deviate from the optimum.
Producing defect-free joints and, more importantly, demonstrating that they are defect-free have associated costs. Although the vast majority of friction stir welds are expected to be free of defects, it is not always possible to assume that they are completely flaw-free. This is especially relevant to the manufacturers aiming to use such welds in highly regulated industries, aerospace in particular. To improve their confidence in the design, manufacture and application of friction stir welds, manufacturers are seeking data on the properties of welds containing flaws and require validated inspection techniques to detect those flaws on-line, after manufacture and in-service.
The major challenge of this project was to perform integrated research to develop the understanding of flaws in friction stir welds and their influence on fatigue performance. In particular, the aim was to generate materials data to relate detectable flaw sizes to mechanical properties of the welds.
Objectives
- Establish the fatigue properties of friction stir welds containing detectable flaws.
- Correlate NDT results (flaw location, characterisation and size) with the fatigue properties of the welds.