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The die casting defects and tensile properties of high pressure die cast (HPDC) Mg‐Zn‐Al‐RE alloys with various combinations of Zn and Al were studied. The results show that die casting defects in Mg‐Zn‐Al‐RE alloys are affected by the percentage of Zn and Al contents. The hot tearing susceptibility (HTS) of Mg‐Zn‐Al‐RE alloys tends to increase with increasing Zn content up to 6 wt%, while a further increase of Al and/or Zn content reduces the HTS. In tensile tests, the yield strength (YS) is generally improved by increasing Zn or Al content, whereas the tensile strength (TS) and ductility appear to depend largely on the presence of casting defects. Compared with Mg‐Zn‐Al alloys, the mechanical properties of the Mg‐Zn‐Al‐RE alloy are significantly improved. The Mg‐4Zn‐4Al‐4RE alloy is found to have few casting defects and the optimal tensile properties.

Magnetic metallic cobalt with different hierarchical structures, such as dendritic particles, flowery particles, and flocky spheres, has been successfully prepared by using a simple solvothermal process in which the relative amounts of H2C2O4and N2H4·H2O in the reaction system were rationally adjusted. The Co crystals with hierarchical structure had a hexagonalclosepacked hcp structure. The dendritic Co crystal comprises several 1–5 μm long dendrites, and thehierarchical assemblies radiate from the center. The flowerlike Co submicrocrystals are composed of petallike crystals around 1.5 μm in diameter and 100–200 nm thick. Interestingly, an intergrade from singlecrystal to polycrystalline structures for flowerlike Co submicrocrystals is observed. The flocky spheres, about 600 nm in diameter, consist of 5 nm thick nanosheets. In addition, a growth mechanism is proposed which is based on the evolution of the structure and morphology with increasing reaction time. Further magnetic measurements for the Co crystals with different hierarchical structures indicated that the morphology of the Co crystals had an obvious influence on their magnetic properties.

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