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 (similar to 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.(c) 2022 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ) Peer review under responsibility of Chongqing University