Aluminum alloys are widely used due to their recyclability, energy efficiency, and corrosion resistance. However, the mechanisms of aqueous corrosion in multicomponent Al alloys remain unresolved. This study investigates the correlation between solute reactivity and the formation of the oxide film during aqueous corrosion of a high-strength Al-Zn-Mg-Cu alloy. The research combines scanning flow cell (SFC), atom probe tomography (APT), aberration-corrected scanning transmission electron microscopy (STEM), and multicomponent Pourbaix diagram calculations. Key findings include the formation of nanocrystalline Al oxide, solute partitioning between the oxide and matrix, and segregation to the internal interface. The Mg content in the oxide layer decreases from 33 at.% in the solution heat-treated state to 15 at.% in the peak-aged alloy, highlighting the impact of heat treatment on oxide stability and corrosion kinetics. Deuterium isotope labeling reveals the presence of D (i.e., H) in the oxide, suggesting that the oxide acts as a kinetic barrier to prevent H embrittlement. These findings advance the understanding of improving Al oxide stability and guide the design of corrosion-resistant alloys.Aluminum alloys are widely used due to their recyclability, energy efficiency, and corrosion resistance. However, the mechanisms of aqueous corrosion in multicomponent Al alloys remain unresolved. This study investigates the correlation between solute reactivity and the formation of the oxide film during aqueous corrosion of a high-strength Al-Zn-Mg-Cu alloy. The research combines scanning flow cell (SFC), atom probe tomography (APT), aberration-corrected scanning transmission electron microscopy (STEM), and multicomponent Pourbaix diagram calculations. Key findings include the formation of nanocrystalline Al oxide, solute partitioning between the oxide and matrix, and segregation to the internal interface. The Mg content in the oxide layer decreases from 33 at.% in the solution heat-treated state to 15 at.% in the peak-aged alloy, highlighting the impact of heat treatment on oxide stability and corrosion kinetics. Deuterium isotope labeling reveals the presence of D (i.e., H) in the oxide, suggesting that the oxide acts as a kinetic barrier to prevent H embrittlement. These findings advance the understanding of improving Al oxide stability and guide the design of corrosion-resistant alloys.