Manganese-enhanced strength and corrosion resistance of extruded Mg-0.7Ca alloys for biodegradable orthopedic implants

Achieving an optimal balance between strength and corrosion resistance remains a significant challenge in the development of biodegradable Mg-Ca alloys for orthopedic applications. The present study investigates the influence of Mn additions at 0.35 and 0.83 wt% on the microstructure, mechanical performance, and corrosion resistance of extruded Mg-0.7Ca alloys. The Mn addition caused substantial grain refinement, significantly reducing the grain size. A moderate Mn addition of 0.35 wt% promoted a fully recrystallized, equiaxed grain structure, whereas 0.83 wt% retained unrecrystallized regions with high local misorientation. Mechanical strength increased with Mn, with peak ductility achieved at 0.35 wt% before declining at higher Mn due to strain accumulation. Immersion and electrochemical tests demonstrated that corrosion resistance improved at 0.35 wt% Mn, supported by its highest charge transfer resistance, but slightly reduced at 0.83 wt% Mn in simulated body fluid (SBF). Time-of-flight secondary ion mass spectrometry analysis revealed Cl⁻ aggregations on the Mn-free and 0.83 wt% Mn alloys, which were not seen on the 0.35 wt% Mn alloy, implying reduced chloride interaction. These findings demonstrate that targeted Mn alloying enables simultaneous enhancement of strength and corrosion resistance, with 0.35 wt% Mn offering an optimal balance option for biodegradable orthopedic implants.