The aim of this paper is to report the very first in situ observations of the deformation behaviour of an Al-Cu alloy in the semisolid state by using ultrafast, high-resolution X-ray microtomography. It is shown that this deformation is non-homogeneous and involves an accumulation of liquid at an intergranular surface nearly perpendicular to the strain axis. Once the liquid is no longer able to feed such a region, micropores form and grow at this surface, finally leading to a crack.

This paper describes the development of a semi-automated friction stir welding (FSW) technique for joining 38 mm nominal outer diameter (OD) tubes of 6082-T6 aluminium alloy with 3.5 mm nominal wall thickness. Process development for this application of FSW required the integration of a rotational axis with the control system of the FSW machine as well as the development of a secondary human-machine interface (HMI) for this axis and also necessitated the design of a retracting tool pin in order to eliminate the exit hole of the pin. Issues relating to tube support, variation in wall thickness and out-of-roundness during welding are not straightforward for thin tube. The main topics covered in this paper are FSW process design and optimisation together with a discussion of the resulting weld zone microstructure. This welding work underpinned a substantial international network project whose aim was to prove the viability of FSW for making high performance joints in extruded aluminium tubes of diameter suitable for fabricating structural components, e.g. for ground vehicles, and to systematically investigate the fatigue performance, fracture paths, associated microstructural changes and mechanical properties under the type of multiaxial loading (biaxial tension-torsion) that tubes might experience in service.