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A preliminary investigation has been carried out into the application of friction stir welding for joining a magnesium alloy to an aluminium alloy. The work has shown that liquation during the welding process can lead to the formation of a brittle intermetallic at the joint interface. This intermetallic has a microstructure composed of a divorced lamellar eutectic containing Al12Mg17 and magnesium. The formation of this microstructure and its influence on mechanical properties are discussed in terms of solidification theory.

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The conservative assumption of residual stress in highly restrained steel structures can lead to unnecessary repairs of defects in welded joints. This applies particularly with respect to high restraint, high yield strength thick sections welds because the assumption of yield strength residual stress is used in integrity assessments. By analysing the stress within components both before and after welding it is anticipated that a greater understanding of the residual stress field as a product of both the welding residual stress and the pre-welding residual stress can be made. This paper discusses a series of experiments designed to build up such a model of the changing stress field within a T-butt weld. Neutron strain scanning has been performed on unwelded flat and curved steel sections and a curved T-butt weld. To complement this, surface X-ray measurements have been carried out in order to gain a quantitative measure of the changing surface stress during welding and sectioning. The findings were that welding stresses dominate close to the weld, bending stresses dominate further from the weld.