The corrosion behaviour of a dissimilar metal friction stir weld between AA2024-T351 and AA7010-T7651 was investigated. Gel visualisation and immersion tests were used to examine the effect of galvanic coupling between the two components. A microelectrochemical cell with a 400 mm diameter glass tip was used to measure the anodic and cathodic reactivities at different positions in the weld region as well as in the base alloys. It was found that the net anodic attack was in the 7010 alloy with the highest susceptibility in the nugget region. The nugget region of 2024 was protected by its high net cathodic reactivity owing to the precipitation of S phase particles.