Effect of Precipitate Evolution on the Pitting Corrosion of Friction Stir Welded Joints of an Al-Cu Alloy

The evolution of precipitates on the top surface of a friction stir welded AA2219-T8 joint was characterized using scanning electron microscopy and transmission electron microscopy. The pitting corrosion of different regions in the joint was investigated by a microcell method and the salt spray test. The pitting corrosion was mainly dependent on the nature of precipitates in each region of the joint. The heat affected zone had the worst susceptibility to pitting corrosion as a result of the presence of coarse θ′ phase, the existence of precipitate-free zones, and the decrease in dissolved Cu in the matrix. However, the thermomechanically affected zone had a slightly improved pitting resistance because θ′ phase redissolved into solid solution. In the shoulder affected zone (SAZ), θ′ and θ phases were completely and partially redissolved, respectively, and the content of dissolved Cu in the matrix increased. As a result, the corrosion resistance significantly increased in the SAZ.