An AA 5052-O alloy was used as the base metal for friction stir welding (FSW). The heat and maximum temperature developed in the matrix of the sample during FSW were computed. Optical observations showed grey strips that appeared on the surface of the sample after anodisation. These grey strips could be attributed to the emergence of a thermomechanically affected zone (TMAZ) from the bulk friction stir welded sample. Mg solubility in the TMAZ increased when Mg(2)Si particles that inherently existed in the matrix of the AA 5052-O alloy dissolved after being subjected to the maximum temperature. In addition, the TMAZ was also subjected to shear stress. Plastic deformation increased the dislocation density. The combined effects of the increased dislocation density and enriched Mg content led to a change in the corrosion resistance and anodic behaviour of this zone.