Key Takeaways & Executive Findings
- •• • Grain size reduction from 181.8 μm to 50 nm via high-speed rolling and Li addition yields a yield strength of 382.2 MPa and ultimate tensile strength of 433.3 MPa in the Zn−3Cu−0.2Sr−0.4Li alloy, enabling load-bearing biodegradable implants that can compete with permanent Ti and Fe devices while avoiding revision surgery. • • The 0.4Li alloy exhibits a 173% increase in yield strength and a 591% increase in elongation compared to the as-cast Li-free alloy, with elongation reaching 15.2%, which addresses the inherent brittleness of as-cast Zn alloys and provides sufficient ductility for orthopedic fixation devices during bone healing. • • Nanocrystalline strengthening contributes 70.4% to the total yield strength of the rolled Zn−3Cu−0.2Sr−0.4Li alloy, establishing grain boundary strengthening as the primary strengthening mechanism and validating HSR as a scalable thermomechanical route for bulk nanocrystalline Zn alloys. • • The fracture mode transitions from brittle in the as-cast 0.4Li alloy to ductile after rolling, indicating that the refined microstructure with dispersed ε, β, and SrZn13 phases effectively blunts crack propagation, which is critical for clinical reliability under cyclic loading.
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Abstract
Bulk nanocrystalline Zn−3Cu−0.2Sr−xLi (x = 0, 0.2, 0.4 wt.%) alloys were fabricated via high-speed rolling (HSR) to address the insufficient mechanical performance of as-cast Zn alloys for biodegradable bone fixation. The HSR process introduced dense dislocations that supplied driving force for recrystallization. Li addition promoted the formation of ε and β phases, which provided abundant heterogeneous nucleation sites and a strong Zener pinning effect, facilitating recrystallized grain nucleation while restricting growth. The average grain size of the 0.4Li alloy was refined from 181.8 μm in the as-cast state to 50 nm after rolling. The rolled 0.4Li alloy achieved an ultimate tensile strength of 433.3 MPa, a yield strength of 382.2 MPa, and an elongation of 15.2%. Relative to the as-cast Li-free alloy, the rolled 0.4Li alloy exhibited a 173% increase in yield strength and a 591% improvement in elongation. Nanocrystalline strengthening was the dominant mechanism, contributing 70.4% to the total yield strength. The fracture mode of the 0.4Li alloy transitioned from brittle fracture in the as-cast condition to ductile fracture after rolling. The combination of alloying design and HSR offers a viable route to bulk nanocrystalline Zn alloys with superior mechanical performance for temporary bone fixation applications.
1. Introduction
Biodegradable metallic implants for temporary bone fixation must provide mechanical support during healing and then degrade without requiring a second surgery. Ti and Fe alloys are non-degradable and often necessitate reoperation to prevent complications such as secondary fractures, osteoporosis, inflammation, and swelling. Mg alloys degrade too rapidly, compromising mechanical integrity before bone union. Zn alloys offer a more favorable physiological degradation rate but suffer from poor mechanical properties in the as-cast state, limiting their clinical adoption. The central bottleneck is the lack of a scalable processing route that can refine the microstructure of Zn alloys to achieve strength and ductility simultaneously.
High-speed rolling (HSR) is an advanced thermomechanical deformation technique that refines microstructures at low cost and high production efficiency. This study applies HSR to Zn−3Cu−0.2Sr−xLi (x = 0, 0.2, 0.4 wt.%) alloys to generate bulk nanocrystalline structures. Li addition promotes ε and β phases that provide heterogeneous nucleation sites and Zener pinning, enabling grain refinement to 50 nm. The resulting alloy achieves a yield strength of 382.2 MPa and elongation of 15.2%, with nanocrystalline strengthening contributing 70.4% to the yield strength. This combination of alloying design and HSR directly addresses the strength–ductility trade-off that has stalled the clinical translation of Zn-based biodegradable implants.
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Ze-xu YANG, Si-cong ZHAO, Lei WANG, Yi-cheng FENG, Er-jun GUO (2026). Microstructure evolution and mechanical properties of bulk nanocrystalline Zn−Cu−Sr−Li alloy processed by high-speed rolling. Transactions of Nonferrous Metals Society of China (中国有色金属学报). https://doi.org/10.1016/S1003-6326(26)67061-6
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Frequently Asked Questions
What is the dominant strengthening mechanism in the rolled Zn−3Cu−0.2Sr−0.4Li alloy, and what is its quantitative contribution?
Nanocrystalline strengthening is the dominant mechanism, contributing 70.4% to the total yield strength of 382.2 MPa. This is attributed to the grain size refinement to 50 nm, which increases grain boundary area and impedes dislocation motion. The remaining contribution arises from secondary phase strengthening and solid solution effects.
How does the fracture behavior of the 0.4Li alloy change after high-speed rolling, and what does this imply for clinical durability?
The fracture mode transitions from brittle in the as-cast state to ductile after rolling, with elongation increasing by 591% to 15.2%. This ductility is critical for withstanding cyclic loads during bone healing and reduces the risk of catastrophic failure in load-bearing applications.
What is the specific role of Li addition in achieving grain refinement during high-speed rolling?
Li promotes the formation of ε and β phases, which increase in volume fraction with Li content. These secondary phases provide abundant heterogeneous nucleation sites for recrystallization via the particle-stimulated nucleation (PSN) mechanism and exert a Zener pinning effect that restricts grain growth, enabling refinement from 181.8 μm to 50 nm.
Can high-speed rolling be scaled for industrial production of nanocrystalline Zn alloys, and what are the cost implications?
High-speed rolling is a low-cost, high-efficiency thermomechanical process suitable for continuous sheet production. The study demonstrates that bulk nanocrystalline Zn alloys can be obtained without complex processing, offering a scalable route for manufacturing temporary bone fixation devices at competitive cost compared to Ti and Fe alloys.
What are the mechanical property benchmarks of the rolled 0.4Li alloy compared to the as-cast Li-free alloy?
The rolled 0.4Li alloy achieves an ultimate tensile strength of 433.3 MPa, yield strength of 382.2 MPa, and elongation of 15.2%. Compared to the as-cast Li-free alloy, this represents a 173% increase in yield strength and a 591% increase in elongation, demonstrating a substantial improvement in both strength and ductility.
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