Corrosion-Associated Mechanical Behavior of Zn-Based Biodegradable Metals During Long-Term In Vitro Immersion Degradation in Hank's Solution

• • Hot-extruded Zn-Cu and Zn-Cu-Fe alloys exhibited significantly suppressed corrosion rates compared to pure Zn during 6-month immersion in Hank's solution, with corrosion current density reduced by up to 40% (from 12.5 μA/cm² for pure Zn to 7.5 μA/cm² for Zn-Cu-Fe), delaying mechanical strength decline by over 30%. • • Alloying with Cu and Fe refined grain size from ~30 μm (pure Zn) to ~5 μm (Zn-Cu-Fe), which mitigated localized corrosion attack, reducing pitting depth by 50% and maintaining 85% of ultimate tensile strength after 6 months versus 60% for pure Zn. • • The presence of Cu and Fe promoted the formation of a protective corrosion product layer composed of ZnO, Zn(OH)₂, and Ca-P compounds, increasing charge transfer resistance from 2 kΩ·cm² (pure Zn) to 8 kΩ·cm² (Zn-Cu-Fe) after 30 days, as measured by EIS. • • Uniform corrosion facilitated by fine second phases (CuZn₅ and FeZn₁₃) reduced stress concentration sites, preserving elongation at break above 10% for Zn-Cu-Fe after 6 months, compared to <5% for pure Zn, crucial for load-bearing implant applications.