Developing new Mg alloy as potential bone repair material via constructing weak anode nano-lamellar structure

The mechanics-corrosion and strength-ductility tradeoffs of magnesium (Mg) alloys have limited their applications in fields such as orthopedic implants. Herein, a fine-grain structure consisting of weak anodic nano-lamellar solute-enriched stacking faults (SESFs) with the average thickness of 8 nm and spacing of 16 nm is constructed in an as-extruded Mg96.9Y1.2Ho1.2Zn0.6Zr0.1 (at.%) alloy, obtaining a high yield strength (YS) of 370 MPa, an excellent elongation (EL) of 17%, and a low corrosion rate of 0.30 mm y⁻¹ (close to that of high-pure Mg) in a uniform corrosion mode. Through scanning Kelvin probe force microscopy (SKPFM), one-dimensional nanostructured SESFs are identified as the weak anode (∼24 mV) for the first time. The excellent corrosion resistance is mainly related to the weak anodic nature of SESFs and their nano-lamellar structure, leading to the more uniform potential distribution to weaken galvanic corrosion and the release of abundant Y³⁺/Ho³⁺ from SESFs to form a more protective film with an outer Ca₁₀(PO₄)₆(OH)₂/Y₂O₃/Ho₂O₃ layer (thickness percentage of this layer: 72.45%). For comparison, the as-cast alloy containing block 18R long period stacking ordered (LPSO) phase and the heat-treated alloy with fine lamellar 18R-LPSO phase (thickness: 80 nm, spacing: 120 nm) are also studied, and the characteristics of SESFs and 18R-LPSO phase, such as the weak anode nature of the former and the cathode nature of the latter (37-90 mV), are distinguished under the same alloy composition. Ultimately, we put forward the idea of designing Mg alloys with high mechanical and anti-corrosion properties by constructing "homogeneous potential strengthening microstructure", such as the weak anode nano-lamellar SESFs structure.