The corrosion susceptibility of friction stir welds in AA2024-T351 was found to vary with the weld processing parameters. Corrosion attack was investigated with in situ X-ray tomography, which showed how the penetration of corrosion into the interior of the structure varied with weld microstructure. The susceptibility to corrosion was related to the degree of overageing by comparing the corrosion behaviour to samples of the base alloy that had been aged at different temperatures. A systematic increase first in the anodic reactivity and then the cathodic reactivity of the overaged structures with temperature can be used to predict the location of the region of the weld with the highest susceptibility to corrosion. Similar investigations were made for a dissimilar weld between AA2024 and AA7010. Laser surface melting produces a thin homogeneous melted and rapidly solidified layer over the weld surface leading to a substantial improvement in corrosion resistance.