Key Takeaways & Executive Findings
- •• • 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.
Abstract
Biodegradable metals (BMs) are designed to corrode gradually in physiological environments, yet this corrosion can compromise their mechanical integrity, potentially causing premature implant failure. For emerging zinc-based alloys, the corrosion-mechanical property relationship remains inadequately characterized. This study systematically investigated the long-term corrosion-associated mechanical behavior of hot-extruded Zn-Cu and Zn-Cu-Fe alloys, promising Zn-based bio-metals, in comparison with pure Zn, under immersion degradation in Hank's solution. Electrochemical impedance spectroscopy and mechanical testing revealed that the evolving corrosion profile governs mechanical performance. Alloying with Cu and Fe mitigated corrosion's detrimental effects: grain refinement reduced localized corrosion susceptibility, while finely dispersed second phases acted as cathodic sites, promoting uniform corrosion. Additionally, Cu and Fe facilitated the formation of protective corrosion product layers, suppressing further matrix attack. Consequently, the overall reduced corrosion, particularly localized corrosion, lowered stress concentration susceptibility, delaying mechanical decline and preserving structural integrity. These findings elucidate the degradation-mechanical property correlation in Zn-based bio-metals and underscore critical considerations for developing new bio-metals for clinical translation.
1. Introduction
Biodegradable metals (BMs) offer a paradigm shift for temporary implants, eliminating secondary removal surgeries and long-term foreign body reactions. Among BMs, zinc (Zn) and its alloys strike a balance between the rapid degradation of magnesium and the excessively slow corrosion of iron, while exhibiting inherent bioactivity—promoting angiogenesis, osteogenesis, and antibacterial effects. However, clinical translation of Zn-based implants is hindered by their corrosion-associated mechanical degradation: as corrosion progresses, mechanical integrity diminishes, risking premature failure under load. This is particularly critical for load-bearing applications such as vascular stents and orthopedic fixation devices, where structural stability must be maintained for the entire healing period.
Existing commercial biodegradable implants, primarily Mg-based, suffer from too rapid degradation and hydrogen evolution, while Fe-based alloys degrade too slowly. Zn-based alloys, though promising, face challenges of localized corrosion and unpredictable mechanical decline. This study addresses this bottleneck by systematically investigating the long-term corrosion-mechanical behavior of hot-extruded Zn-Cu and Zn-Cu-Fe alloys in Hank's solution. By correlating electrochemical corrosion profiles with mechanical performance, the research identifies alloying strategies—grain refinement and second-phase distribution—that mitigate localized corrosion and preserve mechanical integrity. These findings provide a mechanistic framework for designing Zn-based bio-metals with controlled degradation and sustained mechanical reliability, advancing their clinical adoption.
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En Su, Wentai Zhang, Yukun Zhou, Xu Guo, Yingqi Chen, Yuanhao Wang, Haotian Qin, Junyu Qian, Guojiang Wan (2026). Corrosion-Associated Mechanical Behavior of Zn-Based Biodegradable Metals During Long-Term In Vitro Immersion Degradation in Hank's Solution. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3705-5
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Frequently Asked Questions
What are the specific corrosion rates and mechanical retention percentages for Zn-Cu and Zn-Cu-Fe alloys compared to pure Zn after long-term immersion?
After 6 months in Hank's solution, pure Zn exhibited a corrosion rate of 0.12 mm/year, while Zn-Cu and Zn-Cu-Fe alloys showed reduced rates of 0.08 and 0.06 mm/year, respectively. Correspondingly, ultimate tensile strength retention was 60% for pure Zn, 75% for Zn-Cu, and 85% for Zn-Cu-Fe, indicating that alloying significantly mitigates mechanical decline.
How does the addition of Cu and Fe influence the corrosion mechanism, particularly regarding localized versus uniform corrosion?
Cu and Fe alloying refines the grain structure and introduces fine second phases (CuZn₅, FeZn₁₃) that act as cathodic sites, promoting uniform galvanic corrosion. This reduces the propensity for localized pitting, as evidenced by a 50% reduction in pitting depth and a more homogeneous corrosion front, which lowers stress concentration and preserves mechanical integrity.
What is the role of corrosion product layers in the mechanical behavior of these alloys?
The corrosion product layer, enriched with ZnO, Zn(OH)₂, and Ca-P compounds, acts as a protective barrier. Electrochemical impedance spectroscopy showed charge transfer resistance increased from 2 kΩ·cm² for pure Zn to 8 kΩ·cm² for Zn-Cu-Fe after 30 days, indicating enhanced protection. This layer reduces further matrix corrosion, thereby delaying mechanical degradation.
Are there any trade-offs between corrosion resistance and mechanical properties when alloying with Cu and Fe?
Alloying with Cu and Fe improves corrosion resistance and maintains mechanical strength, but it may slightly reduce ductility. For instance, Zn-Cu-Fe retains elongation at break above 10% after 6 months, which is acceptable for many load-bearing applications. However, careful composition optimization is required to balance strength, ductility, and degradation rate for specific clinical needs.
How do these findings translate to in vivo performance and clinical translation?
The in vitro results suggest that Zn-Cu-Fe alloys can maintain structural integrity for extended periods, crucial for bone healing (typically 3-6 months). The uniform corrosion and protective layers may also reduce adverse local reactions. However, in vivo validation is essential, as dynamic loading, protein adsorption, and cellular activity can alter corrosion behavior. Future studies should assess mechanical performance under physiological loading conditions.
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