Corrosion Fatigue of Aluminum Alloys in Chloride Media

The experiments conducted to study the corrosion fatigue for the Al alloys in 3% NaCl at the rest potential show a high resistance for Al 5083 to the rupture compared to Al 6061. The difference between the two alloys is more significant at low stresses. Microscopic examination reveals more, but superficial pitting for Al 5083, whereas in Al 6061, pitting was less but more profound. The application of the anodic polarization for both alloys near the pitting potential resulted in a considerable drop in the resistance to corrosion fatigue compared to the test conducted at the rest potential. The scanning electronic microscope (SEM) reveals the presence of pitting on the lateral surface and near the ruptured surface. These results show that the localized corrosion constitutes an important step in the initiation of corrosion fatigue cracking. SEM fractographs of fracture surfaces reveal transgranular cracks at the rest potential. On the other hand, the intergranular cracks were observed for both alloys at the pitting potential. Photomicrographs, graphs. 19 ref.--AA(UK).