Achieving impressive superplasticity is an important strategy to manufacture Mg alloy products with complex shapes. In the present study, we report that an excellent superplastic deformation with elongation larger than 500% can be achieved at 623 K and 1.0 × 10⁻³ s⁻¹ in a Mg-1.51Zn-0.59Ca-0.59Al-0.70Mn (wt.%, ZXAM2111) alloy fabricated by equal-channel angular pressing. The superplastic deformation is mainly carried by grain boundary sliding (GBS), accompanied by a grain size growth from ~3.0 µm to ~6.0 µm after deformation. Before deformation, the ZXAM2111 alloy is mainly characterized by a strong co-segregation of Zn and Ca atoms at grain boundaries and uniformly distributed β-Mn particles. With deformation proceeding, the β-Mn particles further dynamically precipitate along grain boundaries that parallel the tensile axis, leading to improved resistance to grain coarsening. Although the enhanced stabilizing effects decrease the strain rate sensitivity value, the resulting impressive microstructure stability provides a cornerstone of the active operation of GBS, facilitating the achievement of superplastic deformation. The present work could provide insight into developing low-alloyed Mg alloys with high microstructure thermal stability to achieve superplasticity.

The age-hardening behavior and precipitation evolution of an isothermal aged Mg−5Sm−0.6Zn−0.5Zr (wt.%) alloy have been systematically investigated by means of transmission electron microscopy (TEM) and atomic-resolution high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The Vickers hardness of the present alloy increases first and then decreases with ageing time. The sample aged at 200 ℃ for 10 h exhibits a peak-hardness of 90.5 HV. In addition to the dominant β₀^′ precipitate (orthorhombic, a = 0.642 nm, b = 3.336 nm and c = 0.521 nm) formed on {11-20}α planes, a certain number of γ ” precipitate (hexagonal, a = 0.556 nm and c = 0.431 nm) formed on basal planes are also observed in the peak-aged alloy. Significantly, the basal γ ” precipitate is more thermostable than prismatic β₀^′ precipitate in the present alloy. β₀^′ precipitates gradually coarsened and were even likely to transform into β₁ phase (face centered cubic, a = 0.73 nm) with the increase of ageing time, which accordingly led to a gradual decrease in number density of precipitates and finally resulted in the decreased hardness and mechanical property in the over-aged alloys.

Due to the significant differences in the formation temperature and crystal structure between the primary α-Mg and eutectic β-Mg₁₇Al₁₂, it is a great challenge to achieve simultaneous refinement of the primary and eutectic phases in Mg-Al based alloys via heterogeneous nucleation. Surprisingly, we found that the α-Mg and β-Mg₁₇Al₁₂ in the AZ80 alloy can be simultaneously refined after 0.2 wt.% Sm addition, with the grain size decreasing from ∼217 ± 15 µm to ∼170 ± 10 µm and the β-Mg₁₇Al₁₂ morphology changing from a typical continuous network to a nod-like or spherical structure. The simultaneous refinement mechanism is investigated through solidification simulation, transmission electron microscopy (TEM), and differential thermal analysis (DTA). In the AZ80-0.2Sm alloy, many Al₈Mn₄Sm particles can be observed near the center of the α-Mg grains or inside the β-Mg₁₇Al₁₂. Crystallographic calculations further reveal that the Al₈Mn₄Sm has good crystallographic matching with both the α-Mg and β-Mg₁₇Al₁₂, so it possesses the potency to serve as heterogeneous nucleation sites for both phases. The promoted heterogeneous nucleation on the Al₈Mn₄Sm decreases the undercooling required by the nucleation of the primary and eutectic phases, which enhances the heterogeneous nucleation rate, thus causing the simultaneous refinement of the α-Mg and β-Mg₁₇Al₁₂. The orientation relationships between the Al₈Mn₄Sm and Mg/Mg₁₇Al₁₂ are identified, which are [1210]_Mg//[010]_Al8Mn4Sm, (1010)_Mg//(301)_Al8Mn4Sm and [112]_Mg17Al12//[010]_Al8Mn4Sm, (110)_Mg17Al12//(301)_Al8Mn4Sm, respectively. Furthermore, the refinement of the β-Mg₁₇Al₁₂ accelerates its dissolution during the solution treatment, which is beneficial for cost saving in industrial applications. Other Al₈Mn₄RE compounds such as Al₈Mn₄Y might have the same positive effect on the simultaneous refinement due to the similar physicochemical properties of rare earth elements. This work not only proves the possibility of simultaneously refining the primary and eutectic phases in Mg-Al based alloys via heterogeneous nucleation, but also provides new insights into the development of refiners for cast Mg alloys.

Currently, lithium-ion batteries play a key role in energy storage; however, their applications are limited by their low energy density. Here, we design a facile method to prepare mesoporous ZnMn₂O₄ microspheres with ultrahigh rate performance and ultralong cycling properties by finely tuning the solution viscosity during synthesis. When the current density is raised to 2 A·g^-1, the discharge capacity is maintained at 879 mA·h·g^-1 after 500 cycles. The electrochemical properties of mesoporous ZnMn₂O₄ microspheres are better than that for most reported ZnMn₂O₄. To understand the electrochemical processes on the mesoporous ZnMn₂O₄ microspheres, in situ Raman spectroscopy is used to investigate the electrode surface. The results show that mesoporous ZnMn₂O₄ microspheres have a great potential as an alternative to commercial carbon anode materials.