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Formation and microstructure of banding in a copper friction stir weld was studied using scanning electron microscopy, electron backscatter diffraction, and nanoindentation. Unlike in aluminium, banding only appears in 'cold' friction stir welding (FSW) welds of copper. Banding is formed by layers of small and large grains. It was noticed that higher local misorientations and small grain size correlate in the welds. Owing to differences in the restoration processes of copper and aluminium, texture changes are not visible in copper even though they are in aluminium. Texture of copper FSW welds is weak and independent of the grain structure of the base material, because in the steady state dynamic recrystallisation, the restoration process of copper, the grain structure is mainly dependent of the processing parameters. The hardness differences between the small and large grains are small.

Localization of plastic deformation in different parts (extruded and forged base materials as well as EB and FSW welds) of the corrosion barrier copper canister for final disposal of spent nuclear fuel was studied using tensile testing, optical strain measurement, scanning electron microscopy (SEM), and electron back-scatter diffraction (EBSD). Results show that in the base materials plastic deformation occurs very uniformly. In FSW welds the deformation localizes in the weld either at the processing line or at a line of entrapped oxide particles. In EB welds the deformation localizes to the equally oriented large grains at the weld centreline or at the steep grain size gradient in the fusion line

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