Refined Lamellar Eutectic in Biomedical Zn–Al–Zr Alloys for Mechanical Reinforcement

Zn is recognized as a bone implant metallic material owing to its natural biodegradability and good biocompatibility. In this study, refined lamellar eutectic is constructed in Zn alloys by alloying with Al and Zr via selective laser melting, aiming to improve its mechanical strength. The results demonstrate that lamellar eutectic forms along the grain boundaries due to the alternating solidification of Zn‐ and Al‐enriched phases. The lamellar eutectic not only refine Zn grains but also provide numerous phase interfaces for dislocation pile‐up. More importantly, Al₂ZnZr phase is also found in the alloys and acts as heterogeneous nucleation sites for Al‐enriched phase, which is beneficial for the formation of lamellar eutectic. With Zr content increasing to 0.2 wt%, the amount of Al₂ZnZr phase increases, leading to more lamellar eutectic formation. This reduces the lamellar spacing to 0.34 ± 0.03 µm, providing more phase interfaces for slip interference. As a result, as compared with Zn, the Zn–7Al–0.2Zr alloy presents 179 ± 12% improvement in mechanical strength, which is comparable to the strength criteria for bone implants. In addition, the degradation rate increases from 0.08 ± 0.03 mm year⁻¹ to 0.15 ± 0.03 mm year⁻¹ due to the enhanced galvanic corrosion between Zn‐ and Al‐enriched phases. Cytocompatibility evaluation also indicates that the Zn–7Al–Zr alloys present good biocompatibility to MG‐63 cells.