Intergranular Corrosion Penetration in an Al-Mg Alloy as a Function of Electrochemical and Metallurgical Conditions

An experimental and modeling study of factors influencing intergranular corrosion (IGC) penetration depth into an Al-Mg alloy, AA5083 (UNS A95083), is presented. Potentiostatic tests over a range of potentials in 0.6 M sodium chloride (NaCl) solution were conducted on longitudinal by long transverse (LT), long transverse by short transverse (ST), and longitudinal by short transverse (LS) surfaces of sensitized AA5083. The IGC penetration rate was found to depend on applied potential, degree of sensitization (DoS), exposure time, and propagation direction relative to the rolling direction. Statistical IGC depth distributions were analyzed and served as inputs for a phenomenological model to estimate IGC damage progression for AA5083 during exposure to 0.6 M NaCl solution at pH 8.3. This model was validated by comparing the model predicted and experimental depths for the 100°C sensitization condition. Extension of this combined experimental and modeling approach to the 80°C sensitization demonstrated that sensitization temperature is another significant factor in IGC penetration depths.