The corrosion behavior and microstructure characteristics of metal inert gas (MIG) welded dissimilar joints of the 6005A alloy modified with Sc (designated as 6005A+Sc) and the 5083 alloy were investigated using corrosion tests and microscopy techniques. Results show that the dissimilar joints exhibit strong stress corrosion cracking (SCC) resistance, maintaining substantial strength during slow strain rate tensile tests. Notably, the heat-affected zone (HAZ) and base metal (BM) on the 6005A+Sc side show superior performance in terms of inter-granular corrosion (IGC) and exfoliation corrosion (EXCO) compared to the corresponding zones on the 5083 side. The lower corrosion resistance of the 5083-BM and the 5083-HAZ can be attributed to the presence of numerous Al₂Mg₃ phases and micro-scaled Al₆(Mn,Fe) intermetallics, mainly distributed along the rolling direction. Conversely, the enhanced corrosion resistance of the 6005A+Sc-BM and the 6005A+Sc-HAZ can be attributed to the discontinuously distributed grain boundary precipitates (β-Mg₂Si), the smaller grain size, and the reduced corrosive current density.