Development of biodegradable Mg-Ca alloy sheets with enhanced strength and corrosion properties through the refinement and uniform dispersion of the Mg₂Ca phase by high-ratio differential speed rolling.

A novel processing route was proposed for the fabrication of biodegradable Mg-Ca binary alloys with high Ca contents (2-3 wt.%) in sheet form with enhanced biocorrosion resistance by tailoring their microstructures. The effective refinement and dispersion of the Mg2Ca phase in the Mg-Ca alloys using extrusion followed by high-ratio differential speed rolling (HRDSR) and post-rolling annealing led to the formation of homogeneous microstructures in which submicron-sized and nanosized Mg2Ca particles were distributed over the fine-grained recrystallized matrices with grain sizes of ∼6 μm. The break-up of the Mg2Ca phase into fine and isolated particles and their uniform dispersion in the matrix greatly decreased the susceptibility of individual microgalvanic corrosion between the matrix and Mg2Ca phase and the post-deformation annealing decreased the dislocation density while forming small grains due to the presence of the finely dispersed Mg2Ca particles that reduced the grain sizes by inhibiting grain boundary motion in recrystallization, resulting in a significant improvement in the corrosion resistance of Mg-Ca alloys in Hank's solution. The annealed HRDSR-processed Mg-Ca alloys showed higher corrosion resistance and higher mechanical strength compared with pure magnesium. The processing routes proposed in this study provide a new opportunity for the production of biodegradable magnesium alloy sheets with good strength and corrosion properties.