Influence of an Artificial Ageing on the Corrosion Behavior of AA2024
The corrosion behavior of the 2024 aluminum alloy was studied in a 1M NaCl for samples in the as received T351 metallurgical state and also for samples aged at 150°C for duration time between 0 h and 177 h. Open circuit potential measurements (OCP) showed a strong effect of the ageing treatment on the corrosion behavior of the 2024 alloy with OCP values decreasing when the ageing time increased. An ageing time of 55h was identified as a critical value on the OCP vs ageing time curve. This critical ageing time was also identified on the curves showing the mechanical properties (elongation to rupture, maximal strength) vs ageing time and correlated to a significant evolution of the microstructure by transmission electron microscopy. All the samples, i.e. T351 and aged samples, were submitted to both continuous immersion tests (CI tests) and cyclic corrosion tests (CF tests). A CF test consisted of three cycles of 24 hrs; each cycle was composed of an 8-hr immersion in the electrolyte followed by a 16 hrs air exposure period at -20°C. CI tests, called CI 24 h and CI 72 h, for duration of 24 h and 72 h respectively, were carried out as reference tests. Observations of the samples after the corrosion tests showed that, after CI tests, there was a transition of the corrosion morphology from intergranular to quite transgranular when the ageing time increased: for ageing time longer than 55h, transgranular corrosion was predominant. For all the samples, the corrosion defects morphology was strongly affected by the exposure conditions with CF tests promoting the intergranular corrosion and the branching of the intergranular corrosion defects.
1. C. Augustin, E. Andrieu, C. Blanc, G. Mankowski, and J. Delfosse, J. Electrochem.Soc., 154, C637 (2007).
2. W. Zhang and G. S. Frankel, J. Electrochem. Soc., 149, B510 (2002).
3. C. Larignon, J. Alexis, E. Andrieu, C. Blanc, G. Odemer and J.-C. Salabura. J. Electrochem. Soc., 158, 1 (2011).