In this study, we characterized interfacial mechanisms to better understand the active–passive state for a laser powder-bed-fused (L-PBF) AlSi12 alloy. We compared the additive manufactured microstructures obtained via the L-PBF process vs. the traditional casting method with respect to their influence on corrosion properties. Corrosion resistance was assessed by the damage mechanism based on the corrosion initiation probability and electrochemical behavior in the AlSi12 eutectic alloy. The disconnected silicon network was identified as the vulnerable and lower-corrosion-resistance region in the L-PBF AlSi12 alloy. Without the influence of any additive on the Al-Si alloy system, the damage was correlated with microstructure distortion and mechanical fracturing of the developed oxide structure.