Fabrication of biodegradable materials with high strength by grain refinement of Mg–0.3 at.% Ca alloys

•Severe plastic deformation after Ca alloying contributes to ultra grain refinement.•Minor effects of alloying on the Hall–Petch Parameter are demonstrated.•Mg-Ca alloy with fine grains achieved tensile yield stress over 400 MPa. The effect of grain refinement on the yield stress of magnesium with calcium as the solid solute was investigated. Ultra-grain refinement down to 0.5 μm by extrusion under the controlled Zener–Hollomon parameter resulted in a high tensile yield stress over 400 MPa for biodegradable devices.