| Aluminum alloys such as AA5083 are suitable for marine applications, such as high-speed ships. The high strength-to-weight ratio, excellent weldability, and atmospheric corrosion resistance of AA5083 alloys make them likely candidates for ship structures. Yet, alloys of this kind also have some disadvantages. These alloys are susceptible to intergranular corrosion (IGC) after prolonged exposure at moderate temperature (higher than 50°C). Previous research in this field suggests that Mg-rich beta-phase precipitation on the grain boundary is the sole reason behind such extensive corrosion. In this work, degree of sensitization was quantified at a range of thermal exposure time and temperatures. AA5083 alloy was investigated with H131, O, H116, and H321 tempers. 5456-H116 alloys were also investigated for comparative purposes. ASTM-G67 tests were conducted on the heat-treated alloys to measure their susceptibility to intergranular corrosion. Optical and scanning electron microscopes were used to investigate beta-phase precipitation along the grain boundary, intragranular beta-phase precipitation, and grain size distribution. Scanning transmission electronmicroscopy (STEM) images were captured to identify and estimate the beta-phase growth rate. The STEM images were analyzed to evaluate the beta-phase thickness. Based on the experimental results, a mathematical model was developed which is able to predict the degree of sensitization as a function of exposure time and temperature. This model is extensively utilized in the present work. |
