Improving the ductility of high-strength biodegradable ZnMg alloys through Al, Mn, and Cu microalloying: in vitro evaluation

ZnMg alloys are promising biodegradable materials for orthopedic and cardiovascular implants due to their favorable strength, biocompatibility, and degradation behavior. However, their ductility is often compromised by the brittle Mg₂Zn₁₁ intermetallic phase. In this study, we improved the ductility of high-strength ZnMg alloys through microalloying with Al, Mn, and Cu. Two multicomponent alloys-Zn-0.05 Mg-0.2 Al-0.2 Mn-0.2 Cu (ZA-0.05 Mg) and Zn-0.5 Mg-0.2Al-0.2Mn-0.2Cu (ZA-0.5 Mg)-were designed and compared with binary Zn-0.05 Mg and Zn-0.5 Mg references. Microstructural analysis reveals that microalloying promotes the formation of new Al₁₁Mn₄ and Al₁₀MnZn₈₉ phases, which facilitate grain refinement and contribute to dislocation accumulation. Mechanical tests demonstrate that the ZA-0.05 Mg alloy exhibits the most balanced mechanical properties, achieving yield strength (YS) of 249 ± 1.8 MPa, ultimate tensile strength (UTS) of 319 ± 2.5 MPa, and an elongation of 50.8 ± 2.0%-representing a 31.2% enhancement in ductility over the binary Zn-0.05 Mg benchmark while maintaining higher strength. Microalloying further improves hardness and wear resistance, as reflected in a reduced friction coefficient and lower wear loss. Corrosion tests reveal that the introduced second phases moderately accelerate degradation. The ZA-0.05 Mg alloy exhibits a corrosion rate of 0.495 mm/year (electrochemical) and 0.365 mm/year (immersion), approaching the ideal 0.5 mm/year for orthopedic implants. In vitro biocompatibility assessments confirm excellent cytocompatibility, hemocompatibility (hemolysis rate < 5%), and strong antibacterial performance, even with the incorporation of trace Al. This study provides both theoretical insight and experimental evidence for achieving high strength and high ductility in Zn-Mg-based biodegradable alloys.