A novel core-shell structured Al8Mn4Y-Al2Ca phase and controllable solute-segregation are elaborately designed in dilute Mg-0.6Al-0.5Mn-0.1Ca-0.1Y alloy (wt.%), via incomplete peritectic transformation during twin-roll casting. When soaked in 3.5 wt.% NaCl solution, Al2Ca shell with a low electrochemical potential prevents direct contact of noble Al8Mn4Y with Mg matrix, mitigating the micro-galvanic corrosion and meanwhile accelerating the formation of uniform corrosion film. Thereafter, solute (Al, Ca)-segregation motivates the formation of heterogeneous multilayered corrosion product films, enhancing corrosion resistance and even achieving self-healing upon long-term corrosion. Notably, the dilute Mg alloy exhibits a corrosion rate as low as 0.22 ± 0.05 mm·y−1.