Fatigue and corrosion fatigue behaviors of biodegradable Zn-Li and Zn-Cu-Li under physiological conditions

• The fatigue behaviors of biodegradable Zn alloys were investigated. • The corrosion fatigue behaviors of biodegradable Zn alloys were investigated. • The fatigue fracture mode of biodegradable Zn alloys was analyzed. Zinc (Zn) alloys are emerging as a new class of biodegradable metallic materials due to their good biocompatibility, suitable biodegradability, and nontoxicity. However, the dynamic loading in the human body, along with the corrosive physiological environment, brings great challenges to the application of biodegradable Zn alloys. At present, there are few reports on the fatigue and corrosion fatigue properties of Zn alloys in simulated body fluid (SBF). In the present work, extruded Zn-0.8Li and Zn-2Cu-0.8Li alloys were selected in order to systematically evaluate their fatigue and corrosion fatigue behaviors both in air at ambient temperature and in SBF at 37 °C. Results revealed that the fatigue limits of the extruded Zn-0.8Li and Zn-2Cu-0.8Li alloys were about 135 and 180 MPa, respectively, in air at ambient temperature. However, the fatigue limits of the two alloys decreased to 65 and 80 MPa, respectively, in SBF at 37 °C and showed a linear relationship between the corrosion fatigue life and the stress amplitude. The sources of fatigue cracks in air were internal microstructural defects or weak mechanical properties of the material, while the initiation of corrosion pits on the surface was the main reason for the source of the formation of fatigue cracks in SBF. The fracture mode of the extruded Zn-0.8Li and Zn-2Cu-0.8Li alloys was quasi-cleavage fracturing. Compared to static immersion testing, cyclic loading significantly increased the corrosion rates of the two experimental alloys in a corrosion fatigue environment.