Synergistic Improvement of Mechanical and Corrosion Properties of Mg-9.1Y-1.8Zn Alloys by Hot Extrusion

Magnesium (Mg) alloy is expected to be the promising medical implant material because of its similar strength and Young's modulus to human bone, good biocompatibility and biodegradability. In the present study, as-cast Mg-9.1Y-1.8Zn (WZ92) alloy was homogenized first and then hot extruded to regulate its mechanical and corrosion properties. The as-cast alloy composes of alpha-Mg matrix, Mg24Y5 eutectic phase and interdendritic 18R-long period stacking ordered (LPSO) phase, in which the continuous block- or rod-like 18R-LPSO phase can act as corrosion barrier to prevent the corrosion penetration. After heat treatment, the precipitation of intragranular fine lamellar 14 H-LPSO phase not only reduces the ductility of the alloy, but also provides channels for corrosion intrusion, thus severe corrosion pits are formed. First-principles calculation reveals that the 14 H-LPSO phase is more likely adsorbed with Cl atom, and chemical bonds are formed in the 14 H-LPSO/Cl interface, which results in the worst corrosion resistance of the homogenized alloy. Further extrusion improves the yield strength and ductility (266.7 MPa and 6.8% respectively) of the alloy significantly through fine-grain strengthening, particle dispersion strengthening and kink band strengthening. Meanwhile, the corrosion resistance of the extruded alloy is enhanced through the corrosion barrier effect of long strip LPSO phase, stable product film protection as well as the formation of uniform corrosion mode. This study proves that hot extrusion is an effective method to synergistically improve the mechanical properties and corrosion resistance of WZ alloys, which can provide a favorable reference for the preparation of high-performance medical Mg alloys.