Abstract: Continuously exposure to elevated temperature, known as sensitization, can accelerate the precipitation of the electrochemically active β phase (Al₃Mg₂) at grain boundaries (GBs) in Al-Mg alloys. This results in intergranular corrosion (IGC), which seriously affects the application of Al-Mg alloys in marine environments. Low-angle GBs (< 15°) are considered to restrict the nucleation and growth of the β phase, while high-angle GBs (> 15°) can promote these processes. However, the quantitative relationship between GB misorientation and IGC sensitivity at atomic scale is unknown. Herein, the underlying mechanism of IGC in AA5083 alloys with β phase and GB misorientation is investigated by experiments and simulation. The experimental results show that after sensitization when the misorientation angle exceeded 22.6°, the density of the β phase at GBs reaches up to 50 %-60 %. The hybrid molecular dynamics/Monte Carlo algorithm was utilized to simulate the diffusion of Mg and cluster formation in Al-5Mg alloy with 11 different GB models at 300 and 425 K. The maximum GB misorientation angle insensitive to IGC is about 18.9° to 22.6°. However, at 425 K, this angle decreases to 16.3°, increasing the IGC risk of Al-5Mg alloys. The calculation results provide valuable quantitative guidance for the corrosion resistance design of Al-Mg alloys.

Key words: Aluminum, EBSD, Molecular dynamics, Diffusion, Intergranular corrosion