MODELING AND PREDICTION OF ASTM-G67 CORROSION DAMAGE IN AA5083-H131 ALLOYS

The AA5083 alloys are widely used for marine application. However, these alloys are susceptible to intergranular corrosion (IGC) after prolonged exposure at elevated temperature. Formation of Mg rich beta phase (Al₃Mg₂) is the primary concern in this type of material degradation. In this work, we investigated Mg diffusion behavior to quantify the amount of beta phase formation. AA5083 alloy was investigated with H131 temper. ASTM G67 mass loss tests were performed to evaluate the degree of sensitization and high resolution scanning electron microscopy (HRSEM) images were taken to investigate the beta phase growth rate. Etch trench thickness was measured from the HRSEM images.Beta phase thickness was estimated from the etch trench thickness distribution profile. An empirical correlation was established between beta phase thickness (at specific heat treatment temperature and exposure time) and corresponding ASTM G67 mass loss values. A model was developed following the fundamental theory of diffusion that can also evaluate the beta phase thickness for a specific thermal exposure time and temperature. The model works based on the theoretical assumption that increase in Mg concentration at the grain boundary (due to formation of beta phase) is equal to the decrease in concentration of Mg close to the grain boundary region. The empirical correlation of beta phase thickness and mass loss was used in the model to predict the ASTM G67 corrosion damage of AA5083 alloys for a range of thermal exposure time and temperature.Model predicted mass loss values match reasonably well with the ASTM G67 test results.