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.

It has been well known that doping nano-scale catalysts can significantly improve both the kinetics and reversible hydrogen storage capacity of MgH₂. However, so far it is still a challenge to directly synthesize ultrafine catalysts (e.g., < 5 nm), mainly because of the complicated chemical reaction processes. Here, a facile one-step high-energy ball milling process is developed to in situ form ultrafine Ni nanoparticles from the nickel acetylacetonate precursor in the MgH₂ matrix. With the combined action of ultrafine metallic Ni and expanded graphite (EG), the formed MgH₂Ni-EG nanocomposite with the optimized doping amounts of Ni and EG can still release 7.03 wt.% H₂ within 8.5 min at 300 ℃ after 10 cycles. At a temperature close to room temperature (50 ℃), it can also absorb 2.42 wt.% H₂ within 1 h. It can be confirmed from the microstructural characterization analysis that the in situ formed ultrafine metallic Ni is transformed into Mg₂Ni/Mg₂NiH₄ in the subsequent hydrogen absorption and desorption cycles. It is calculated that the dehydrogenation activation energy of the MgH₂Ni-EG nanocomposite is also reduced obviously in comparison with the pure MgH₂. Our work provides a methodology to significantly improve the hydrogen storage performance of MgH₂ by combining the in situ formed and uniformly dispersed ultrafine metallic catalyst from the precursor and EG.