Al-Cu-Mg-Si is a commonly used high-strength cast aluminium alloy series; however, the presence ofCu-containing phases causes severe pitting in chloride-containing environments, which significantly limits its applicationpotential. In the present work, the initiation and propagation of pitting in cast Al-5.6Cu-0.3Mg-0.3Si alloys weresystematically analysed by observing corrosion morphologies via SEM combined with electrochemical analysis. Thedevelopment of a high-pit resistance alloy was achieved by the addition of Cr or Zr. The results indicate that the initiationof pitting occurs at Cu-containing phases and that the propagation of pitting occurs along grain boundaries. The size ofpitting is correlated with the distribution of Cu-containing phases, and the addition of Cr or Zr significantly reduces the sizeof Cu-containing phases present at grain boundaries by grain refinement, thereby reducing the size of pitting. Comparedwith the base alloy, the addition of Cr or Zr increaseds the equivalent thickness of the passive films by 112% and 171%,respectively, and the substantial increase in charge transfer resistance is the primary factor in inhibiting interfacialelectrochemical reactions. The alloy with 0.2 wt.% Zr addition exhibiteds decreases in the corrosion current density,maximum pitting depth and pitting area of 68.7%, 48.0% and 74.8%, respectively