Sensitization of Naturally Aged Aluminum 5083 Armor Plate

A sample of aluminum armor plate, approximately 40 to 50 years old, containing a large intergranular stress corrosion crack was evaluated. Scanning electron microscopy examination of the fracture surfaces is consistent with intergranular stress corrosion cracking and some evidence of variable environmental and stress history is noted. ASTM G-67 nitric acid mass-loss values were 19 to 25 mgcm2. The transmission electron microscopy microstructure of the sample was found to be consistent with sensitization due to aging at low temperatures for a long time. The grain boundary magnesium-rich phase is continuous, although non-uniform, and only 10 to 15 nm thick.