Implants are inevitably subjected to stress corrosion, bringing serious challenges to the controlled degradation of biomedical Mg alloys. It is worth studying the stress corrosion cracking (SCC) behavior of Mg alloy and exploring Mg alloy with good SCC resistance for wide biomedical applications. In this work, the as-cast and as-extruded Mg-3Gd-1Zn-0.4Zr (GZ31K) alloys with uniform corrosion were used to investigate SCC behavior. The as-extruded GZ31K alloy exhibited better corrosion resistance and mechanical properties than the as-cast one mainly owing to grain refinement and uniformly distributed fine precipitates, and possessed superior SCC resistance. To clarify the SCC mechanism, the slow strain rate tests were assisted with applied constant potentials via an electrochemical workstation. Accelerated anodic dissolution at anodic polarization deteriorated SCC resistance due to the initiation of corrosion pits and micro-cracks. However, cathodic polarization had no obvious effects on SCC resistance, along with both retarded corrosion and accelerated hydrogen evolution. Stacking faults in GZ31K alloy were hydrogen capture containers to reduce the effect of hydrogen on SCC resistance during cathodic polarization. These findings provide new insights into the evaluation of SCC mechanism, and offer more opportunities to explore Mg alloys with good SCC resistance by regulating anodic dissolution.

Low-alloyed magnesium (Mg) alloys have emerged as one of the most promising candidates for lightweight materials. However, their further application potential has been hampered by limitations such as low strength, poor plasticity at room temperature, and unsatisfactory formability. To address these challenges, grain refinement and grain structure control have been identified as crucial factors to achieving high performance in low-alloyed Mg alloys. An effective way for regulating grain structure is through grain boundary (GB) segregation. This review presents a comprehensive summary of the distribution criteria of segregated atoms and the effects of solute segregation on grain size and growth in Mg alloys. The analysis encompasses both single element segregation and multi-element co-segregation behavior, considering coherent interfaces and incoherent interfaces. Furthermore, we introduce the high mechanical performance low-alloyed wrought Mg alloys that utilize GB segregation and analyze the potential impact mechanisms through which GB segregation influences materials properties. Drawing upon these studies, we propose strategies for the design of high mechanical performance Mg alloys with desirable properties, including high strength, excellent ductility, and good formability, achieved through the implementation of GB segregation. The findings of this review contribute to advancing the understanding of grain boundary engineering in Mg alloys and provide valuable insights for future alloy design and optimization.

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.