Al-Mg alloys are seeing increasing application in naval and automotive industries due to their high strength-to-weight ratio and excellent corrosion resistance. However, these alloys are susceptible to sensitization at elevated temperatures, resulting in localized corrosion and stress corrosion cracking at the grain boundaries. In this study, we combine electron backscatter diffraction (EBSD) with corrosion and stress corrosion cracking experiments to relate microstructural characteristics to susceptibility to localized attack. This approach facilitates the rapid exploration of thousands of grain boundaries. In addition to the grain boundary and crystallographic orientation information, EBSD also provides insight into the local density of geometrically necessary dislocations. Our results show that localized accumulation of dislocations at grain boundaries promotes Mg-rich β-phase formation, increasing the susceptibility to stress corrosion cracking. We show that even low angle grain boundaries, which are traditionally considered resistant to sensitization, can form β-phase in the presence of local dislocation accumulation.