AbstractThe industrialisation of Mg alloys is hindered by low strength and ignitability. In this way, compressive strength is of prime interest, and unfortunately, commercial Mg castings have compressive yield strength less than 200 MPa. We have developed a non-ignitable Mg–0.36Al–1CaO (wt.%) alloy by ECO processing route that, despite its leanness (<1 wt.% total alloying content), has a compressive yield strength of higher than 200 MPa in all three different conditions of as-cast, T4, and peak-aged T6, showing the viability of both age hardening, and solid-solution strengthening accompanied by short-range order. The chemical analysis revealed that the reaction between 1 wt.% of added CaO and the melt led to ~0.4 wt.% alloyed Ca (Ca/Al mass ratio is ~1). The protective effect of alloyed Ca, enabled casting without extra protections (gases or salt) with no sign of ignition. Microstructural evolution was studied by SEM and EDS in conjunction with thermodynamic calculations. Comparison of the compressive yield strength of this alloy (in as-cast, T4, and peak-aged T6 conditions) with that of commercial alloys showed this alloy has the highest strength, with the added benefits of lower production costs and ignition resistance, bestowed by utilising cheap CaO.