The corrosion behavior of Mg‐0.6%Si‐2%Zn alloys in simulated body fluid was studied to understand the time-dependent processes and interfacial phenomena. The alloy's microstructure includes Mg-rich dendrites within eutectic microconstituent. Electrochemical responses showed minimal dependence on dendritic-spacing. Initial immersion (12.2-hour) formed a protective layer, indicated by potential elevation, polarization resistance escalation, and changes in Nyquist and Bode plots. However, between 12.2- and 168.4-hour, the protective layer integrity decreased, with observable corrosion. The corrosion mechanism involved protective layer formation followed by cracking induced by Pilling-Bedworth ratio and high H2 evolution kinetics. This time-dependent corrosion resistance resembles both corrosion-resistant and corrosion-sensitive Mg alloys, showcasing challenges in accurate assessment.