Surface Orientation Dependent Corrosion Damage and Temperature Dependent Mechanical Property Degradation of Sensitized AA5083-H116 Alloys
Mills, Robert Jeffrey
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This study relates the sensitization process microstructural changes of 5083-H116 to its resulting corrosion resistance and mechanical performance. Alcoa 5083-H116 was sensitized in an environmental chamber at 100°C for up to ~1500 hours and 150°C up to ~2000 hours, revealing different degrees of sensitization based on exposure times. Microstructural characterization was conducted on etched sensitized samples. Additionally, samples were subjected to accelerated corrosion scenarios for subsequent microstructural examination and subsequent mechanical (tension and tensile creep) testing. To connect the laboratory studies to the field exposure, Novelis 5083-H116 was sensitized at 100°C; dog bone samples were created and exposed for two years in a beach environment to investigate possible sensitization and corrosion effects. It was found that the sensitization at 100°C and 150°C of Alcoa 5083-H116 led to recrystallization from the asreceived (AR) state of the material (3 mg/cm²). The degree of sensitization of 61 mg/cm² recrystallized the grain size the most from the AR state. The higher sensitization temperature of 150°C caused higher thickness loss and mass-loss rates (MR) for the intergranular corrosion (IGC) susceptible sensitization levels. Accelerated corrosion on different surface orientations led to different corrosion mechanisms (parallel IGC vs. perpendicular IGC). While 5083-H116 material corroded on the rolled surface led to a uniform exfoliation damage on 150°C sensitization exposure, the 100°C rolled surface only exhibited pitting corrosion damage. The through plate thickness corrosion damage, however, exhibited a corrosion susceptible-resistant-susceptible (CSRS) pattern. Mechanical properties were assessed for the various conditions in terms of room temperature tension testing and elevated temperature creep tests. Sensitization affected yield strength but did not play a role in ultimate tensile strength. The presence of corrosion damage lowered yield strength and ultimate tensile strength of the IGC susceptible sensitized 5083-H116, with the through thickness corrosion damage reducing the properties more than corrosion of the rolled surface. Material sensitized at 150°C and then corroded had a greater reduction in room temperature mechanical properties. Creep testing was performed at elevated temperatures, and it was found the solely sensitized 5083-H116 at 100°C or 150°C behaved the same as as-received 5083-H116. When corrosion damage was introduced, creep rupture times and secondary creep rates were changed. Once the corroded section area was accounted for, no significant difference in Larson-Miller parameters was observed.
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