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Characterization of Aluminum Magnesium Alloy Reverse Sensitized via Heat Treatment

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Technical Report

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Naval Postgraduate School Monterey United States

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This research explores a novel repair technique to reverse the sensitization of aluminum magnesium Al-Mg alloys. Al-Mg alloys can become sensitized when magnesium comes out of solution as a second phase, Al3Mg2, on the grain boundaries, eventually forming a continuous network and increasing susceptibility to intergranular stress corrosion cracking SCC. Sensitized 5456 Al-Mg alloy samples removed from active Navy ships were metallographically characterized. These were compared to similar samples that were heat treated in order to reverse the sensitization effect. Both of these were also compared to as wrought 5456 aluminum. All samples were also tested for tensile strength and degree of sensitization using the ASTM G67 Nitric Acid Mass Loss Test NAMLT.Two heat treatment profiles were compared. Both of these profiles successfully reversed the sensitization effect, with similar performance. Heat treatment may have affected the tensile properties and negatively degraded the resulting microstructure by annealing the material. Therefore, more research is necessary to prove this techniques suitability for shipboard repair.

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