Exfoliation corrosion susceptibility in the zones of friction stir welded AA2098-T351

In the present study, the exfoliation susceptibility of the weld zones in friction stir welded AA2098-T351 was compared with that of the base metal (BM) according to ASTM G34 standard practice. Friction stir welding (FSW) had a significant effect on the microstructure of the Al alloy tested and the susceptibility to exfoliation was strongly affected by the microstructure. Different features of corrosion attack and exfoliation susceptibility were observed when the zones affected by FSW were tested isolated or coupled. Also, the near-surface deformed layer had an important effect on the Al alloy susceptibility to exfoliation. These are the main findings of this work. The corrosion features were correlated with the microstructural modifications related to the welding process and with the electrochemical response. The T1 phase morphology, distribution and size were critical for exfoliation susceptibility. The stir zone (SZ) was the zone most resistant to exfoliation. However, resistance to exfoliation varied with the temperatures reached in the heat affected zones (HAZs). The HAZ exposed to the lowest temperatures during welding, HAZ (LT), was the most susceptible to exfoliation, whereas the HAZ exposed to the highest temperatures, HAZ (HT), presented high resistance to exfoliation, similarly to the SZ. The ASTM-G34 practice was an effective and useful method in identifying the different exfoliation resistances of the BM and the various zones affected by FSW. The results of this practice were supported by electrochemical impedance spectroscopy (EIS) tests. (C) 2019 The Authors. Published by Elsevier B.V.