Al 5XXX series aluminum alloys are being used in naval military applications, and being exposed to outdoor environments. With sufficient time and temperature exposure, these alloys undergo a process in which a secondary B phase forms at the grain boundary that sensitizes the alloy to stress corrosion cracking. The relationship between this sensitization and the microstructural features of Al 5083-H116, 5083-H131, 5083-H321, 5456-H116 aluminum alloys, such as grain boundary misorientation angle, dislocation densities, and B phase nucleation densities were examined and reviewed. Samples were aged for up to 30 months at varying temperatures (40°C, 50°C, 60°C, and 70°C), then analyzed using the ASTM G-67 mass loss test. Grain size and grain boundary information were collected via electron backscatter diffraction (EBSD). Geometrical dislocation density information was calculated from the EBSD data. SEM and AFM data were used to determine B phase nucleation density values. Grain boundary misorientation angle, grain size, and dislocation density were found to influence the B phase nucleation density and rate of sensitization. These features were correlated with the mass loss tests performed on these alloys at varying degrees of sensitization. A model was built to simulate the effects of these different factors on the sensitization rate and outcome of the mass loss tests.
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