<i>Ab initio</i> study of precipitate stability in an Mg–Zn–Zr–Y alloy and its effects on corrosion, antimicrobial and <i>in vitro</i> biocompatibility

Magnesium (Mg) alloy has long been projected as a degradable biomaterial with a special focus on its corrosion behaviour, mechanical properties and biocompatibility. In this study, we developed an Mg-5Zn-0.5Zr-0.9Y alloy and studied the effects of Mg₇Zn₃ and Mg₂₄Y₅ precipitates on its mechanical, corrosion, antimicrobial, and <i>in vitro</i> biocompatibility properties. The cast specimen exhibited a continuous network of Mg₇Zn₃ precipitates and a weaker basal texture, which adversely affected the mechanical and corrosion properties. The application of thermomechanical treatment preferentially dissolutes the Mg₇Zn₃ precipitate network compared to the Mg₂₄Y₅ precipitate owing to its lower cohesive energy, lower enthalpy of formation and lower bonding electrons, as calculated using the first principle study. This resulted in a significant reduction in the volta potential difference between the precipitates and the matrix, which simultaneously improved corrosion resistance and ductility. Moreover, the increased area fraction of Mg₂₄Y₅ fine precipitates in the forged specimen contributed to its enhanced corrosion resistance. DFT calculations indicated a lower total density of state (DOS) value near the Fermi energy level of Mg₂₄Y₅, which retarded electron loss capability and thereby reduced the corrosion rate. The higher corrosion resistance of the forged sample was due to lower defect density, as determined through Mott-Schottky analysis. All samples exhibited excellent antimicrobial properties against Gram-negative <i>E. coli</i> bacteria. Improved degradation properties of the forged specimen enhanced cell viability and alkaline phosphatase activity against MC3T3-E1 cells, indicating its non-toxic nature.