Micro arc oxidation (MAO) coatings were applied on friction stir welds of aluminum alloys to improve their corrosion resistance. Uncoated and MAO coated welds were subjected to salt spray corrosion. Studies revealed severe corrosion in uncoated welds, particularly in their thermomechanically affected and heat-affected zones. MAO-coated welds showed no signs of corrosion. The results suggest that the corrosion resistance of friction stir welded aluminum alloys can be substantially improved by applying MAO coatings. © 2008 Acta Materialia Inc.