Stress Corrosion Cracking of Al-Mg Alloy 5083 Sensitized at Low Temperature

Intergranular stress corrosion cracking (IGSCC) in Al-Mg alloy 5083-H131 is characterized for slow-rising stress intensity loading in NaCl solution at a near-open circuit potential. The susceptible S-L orientation isolates the controlling-deleterious effect of grain boundary β (Al₃Mg₂) precipitates. Low-temperature sensitization produces severe IGSCC, provided that the degree of sensitization (DoS, measured by nitric acid mass loss) is above a critical level of 9 mg/cm² to 12 mg/cm². Fatigue precrack tip intergranular corrosion occurs, threshold stress intensity for IGSCC falls, and Stage II crack growth rate rises as single functions of mass loss for sensitization at 60°C, 80°C, or 100°C. The DoS dependence of IGSCC is explained with the coupled crack tip dissolution-hydrogen environment embrittlement mechanism. IGSCC occurs above a critical DoS when the amount of β dissolution is sufficient for hydrolytic-crack acidification promoting H uptake and α boundary embrittlement, as quantified in a companion paper. Microscale stress concentration from nondeformable grain boundary β promotes fracture process zone H enrichment, decreased-critical H concentration, and increased H diffusivity, which collectively sustain fast-subcritical IGSCC rates.