Abstract: Interactions of solute atoms in biodegradable zinc alloys and their effect on alloy mechanical properties have been less investigated. In this work, the interactions between the common solutes (Li, Mg, Mn, Cu, and Ag) used in the biodegradable Zn alloys, including a solute-solute pair with the same element or with two different elements, are investigated based on first-principles calculations. It is found that the energetically favorable configuration is the third nearest-neighboring for most solute-solute pairs in the bulk lattice because of the relatively strong electronic interaction between solute and Zn atoms or the relatively small local elastic deformation associated with the configuration. Considering that interfacial cleavage is a key fracture mode of zinc, the segregation ability of these solutes and their effect on the {101¯2} twin boundary cohesion are also examined. The result shows that Li tends to fully occupy its preferred site in the twin boundary, while Mg, Mn, Cu, or Ag has a concentration limitation in the twin boundary. The twin boundary cohesion can be significantly enhanced by the segregation of Mn, followed by Cu and Ag, because of the contribution of their d states close to the Fermi level. Furthermore, the co-segregation ability of two solute atoms in the twin boundary increases with increasing the binding tendency of these two solute atoms in the boundary. Mn and Li or Mg show a relatively strong co-segregation ability in the twin boundary. Adding Mn to Zn-Li or Zn-Mg alloys can significantly enhance the resistance to fracture of twin boundaries.

Key words: Zinc alloys, Twin boundary, Solute-solute interaction, Co-segregation, Interfacial fracture