Microstructures and bio-corrosion resistances of as-extruded Mg–Ca alloys with ultra-fine grain size

Electrochemical and immersion tests were conducted to characterize the bio-corrosion resistance of as-extruded Mg–Ca binary alloys with submicron grain size. The microstructures were further characterized by optical microscopy (OM), scanning electronic microscopy and transmission electron microscope (TEM). The grain size was estimated from OM and TEM images. Three samples and at least 20 images were used to evaluate the average grain size. Macro-textures of the as-extruded samples were measured via X-ray diffraction. The Mg–2Ca alloy extruded at 300 °C (2Ca-300) exhibits the lowest current density of 1.683 mA·cm⁻² and corrosion rate of 22.14 g·m⁻²·day⁻¹ in simulated body fluid, which is comparable with that of pure Mg. The Ca addition can reduce grain size of as-extruded Mg alloy and decrease the corrosion rate. The formed Mg₂Ca phases would accelerate the local galvanic corrosion and protect the α-Mg matrix simultaneously due to the lower electrode potential. The lower defect density, finer grain size and weaker basal texture intensity contribute to the excellent bi-corrosion resistance of the 2Ca-300 alloy.