Corrosion Behavior Of Friction Stir Welded Joint Of High Strength Aluminium Alloys

The corrosion behaviors of friction stir welded joints of 2024 and 7075 high strength aluminium alloys under different environments had been evaluated. This research was significant for developing the application of friction stir welding in high strength aluminium alloys.The comparative study of the corrosion behaviors of friction stir welded joints of two alloys were carried out by neutral salt spray test, acid salt spray test, immersion test and stress corrosion test. The test cycle time were 8 h, 32h, 72h, 144h, 168h and 240h, respectively. The microstructures of the samples were observed through the optical microscope and TEM. The appearance of corroded regions and the corrosion product were observed and analyzed by using of SEM with EDS. The corrosion mechanism of friction stir welded joints was discussed.The results showed that the nugget zone was less susceptible to corrosion under all corrosion environments, and the advancing TMAZ was more susceptible to corrosion than the retreating TMAZ. During neutral salt spray test and acid salt spray test, Pitting corrosion was initially appeared in the samples of two alloys, subsequently was changed to intergranular corrosion and exfoliation corrosion. But the intergranular corrosion of 7075 samples was more severe, and quickly developed to exfoliation corrosion. It was indicated that 7075 samples were sensitive to intergranular corrosion. The corrosion in acid salt spray test is faster than in neutral salt spray test. The corrosion type of 2024 samples was mainly pitting corrosion and 7075 sample was mainly intergranular corrosion in immersion test. Exfoliation corrosion was appeared in stress corrosion test and the crack was appeared in the corrosion product layer.