Corrosion Fatigue of Al 5083-H131 Sensitized at 70, 100, and 175C and Relation to Microstructure and Degree of Sensitization

Corrosion fatigue thresholds of Al 5083-H131 at high load ratio do not degrade until the ASTM G67 mass loss exceeds approximately 30 mg/cm², regardless of aging temperature.  For mass loss greater than 30 mg/cm², the rate of degradation of the corrosion fatigue threshold with mass loss is independent of aging temperature. The critical mass loss for corrosion fatigue threshold degradation, 30 mg/cm², is associated with the occurrence of a semi-continuous type of grain boundary coverage by β Al₃Mg₂. Once the grain boundary is fully covered with β, typically in the ASTM G67 mass loss range of 40 to 50 mg/cm², the threshold has already degraded substantially. Some of the practical implications of these findings are that the existence of a critical degree of sensitization for corrosion-fatigue degradation can serve as a structural risk management criterion, and the aging temperature independence of this critical degree of sensitization suggests an accelerated aging method for quality control for manufacture and procurement of Al-Mg alloys.