Influence of magnesium addition on microstructural and mechanical stability of hydrostatically extruded biodegradable zinc alloys

Pure and low-alloy zinc holds significant potential for use in biodegradable devices, such as coronary stents. However, its thermal stability has not yet been thoroughly characterized. This study focuses on the effect of magnesium addition on the mechanical and microstructural stability of zinc alloys with 0.6 and 1.3 wt% Mg, subjected to hot extrusion and hydrostatic extrusion. Pure zinc was used as a reference material to provide a comprehensive comparison. Electron Backscatter Diffraction (EBSD) analysis revealed that the addition of magnesium enhanced thermal stability by forming intermetallic Mg₂Zn₁₁ phases, that hindered grain growth as compared with pure zinc. The Zn-0.6 Mg alloy exhibited faster static recrystallization compared to the Zn-1.3 Mg alloy, attributed to its lower initial average grain size and higher density of low-angle grain boundaries. These microstructural changes correlated with mechanical properties, as all materials showed increased strength after heating to 50 °C, which was attributed to dislocation annihilation and the formation of low-angle grain boundaries, as observed through transmission electron microscopy (TEM). Static compression tests demonstrated that the Zn-1.3 Mg alloy maintained a high compressive yield strength of ≈350 MPa, even after heating to 150 °C, highlighting its potential for safe future processing into stents.