Influence of Si on Dispersoid Precipitation Behaviors and Its Impact on Corrosion Resistance in a 5xxx Al─Mg─Mn Alloy

5xxx series Al─Mg─Mn alloys are known for their excellent corrosion resistance. However, when the Mg content exceeds 3.5 wt.%, the corrosion resistance deteriorates significantly. This study elucidates how Si, as an alloying element, enhances the corrosion resistance of 5xxx aluminum alloys by influencing the precipitation of dispersoids. The addition of Si significantly accelerated the precipitation kinetics of dispersoids through two main mechanisms: first, by providing heterogeneous nucleation sites via metastable Mg 2 Si precipitates for α‐Al(Mn, Fe)Si and Al x (Mn, Fe) dispersoids; and second, by promoting the formation of α‐Al(Mn, Fe)Si dispersoids, which precipitate more actively than the Al x (Mn, Fe) phase. Results from the nitric acid mass loss test and potentiodynamic polarization curves demonstrated a significant improvement in corrosion resistance in the Si‐modified alloy. Microstructural analysis revealed that in the Si‐free alloy, the Al 3 Mg 2 phase formed a continuous grain‐boundary network, which acted as a pathway for intergranular corrosion. In contrast, in the Si addition alloy, dispersoids disrupted this continuous network. Furthermore, in Si‐modified alloy grain‐boundary precipitation of Al 3 Mg 2 is likely restricted owing to local sequestration of solute Mg within grains via two microstructural pathways: heterogeneous nucleation of intragranular Al 3 Mg 2 on dispersoids and formation of metastable Mg 2 Si precipitates along dislocation tangles stabilized by dispersoids.