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

Abstract

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 Mg 2 Zn 11 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. • Hydrostatic extrusion creates a stable microstructure upon heating up to 150 °C for the Zn-Mg alloys. • Mg 2 Zn 11 intermetallic phase inhibits grain growth and, consequently, static recrystallization in hydrostatically extruded Zn-Mg alloys. • The differences in the mechanical properties upon heating were related with changes in low angle grain boundaries. • Mg content should be carefully selected in Zn-Mg alloys to prevent instability during future manufacturing.

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