Zn Alloy Biodegradation in Implants: Corrosion Mechanisms and Mitigation

Biodegradable Zn‐based alloys have attracted increasing attention as materials for biomedical implants because they offer moderate degradation rates and favorable biocompatibility compared with Mg‐ and Fe‐based alloys. In physiological environments, their degradation is governed by electrochemical corrosion and typically involves uniform corrosion, microgalvanic corrosion‐driven localized attack, stress‐assisted corrosion cracking, and corrosion fatigue under mechanical loading. Corrosion behavior is jointly governed by microstructural factors, including intermetallic compounds, grain structure, boundaries and interfaces, and the evolution of corrosion‐product layers. It is also influenced by environmental factors, such as Cl − concentration, pH, and organic and biological species, which together determine corrosion thermodynamics, kinetics, and degradation mechanisms. Microalloying, thermomechanical processing, and surface coatings or modifications can tailor phase constitution, microstructure, and interfacial reactions, thereby suppressing localized corrosion and improving the controllability of degradation. Although substantial progress has been made in understanding their degradation mechanisms, structural and chemical heterogeneities in these alloys continue to promote localized corrosion and stress‐assisted failure in an unpredictable manner. Moreover, the strong environmental dependence of corrosion limits the ability to achieve on‐demand degradation. Future research should focus on microstructure optimization, surface and interface engineering, and environment‐adaptive design to achieve stable, controllable, and predictable degradation of Zn‐based alloys for biomedical applications.