Friction stir welding of thick section aluminium alloys
By Georges Brooks (Sheffield Hallam University, TWI Ltd), Alan Smith (Sheffield Hallam University), Steven Magowan (Sheffield Hallam University), Stephen Cater (TWI Ltd), Jeroen De Backer (TWI Ltd)

Friction stir welding (FSW) is a solid state joining technology with a wide range of applications. However, there is a limited pool of published knowledge relating to FSW in thick section materials and the process variants that make this possible. FSW of aluminium alloys of 50mm or greater thickness requires specialist equipment which limits the opportunities for investigating such material geometry.
The primary aim of the research project is to investigate the influence of welding variables on the microstructure, mechanical properties and corrosion resistance of welds created in thick section aluminium. To do this, three distinct FSW techniques; weld-flip-weld (WFW-FSW), simultaneous double sided (SDS-FSW) and supported stationary shoulder (SSS-FSW) are to be used in 50mm thick AA5083-H111, AA6082-T651 and AA7050-T7451. Each of the three process variants has different thermo-mechanical inputs to the weld zone which have yet to be extensively investigated and quantified.
This is a work in progress, having commenced in October 2018. Up to this point, energy input to the weld zone has been calculated and micro-hardness mapping and energy dispersive X-ray spectroscopy have been undertaken to establish mechanical and microstructural property changes between the parent and welded material. Future work will encompass full section tensile testing, hardness mapping and electron back scatter diffraction (EBSD) of both the as welded and naturally aged samples. In addition to this, tool wear will be investigated using an infinite focus microscope to measure the influence of welding on tool thread depth, tool length and tip diameter.