Journal of Magnesium and Alloys最新文献

The high cost of using the niobium (Nb) barrier for manufacturing magnesium diboride (MgB₂) mono-and multi-filamentary wires for large-scale applications has become one of the barriers to replacing current commercial niobium-titanium superconductors. The potential of replacing the Nb barrier with a low-cost iron (Fe) barrier for multifilament MgB₂ superconducting wires is investigated in this manuscript. Therefore, MgB₂ wires with Fe barrier sintered with different temperatures are studied (from 650 °C to 900 °C for 1 h) to investigate the non-superconducting reaction phase of Fe-B. Their superconducting performance including engineering critical current density (J_e) and n-value are tested at 4.2 K in various external magnetic fields. The best sample sintered at 650 °C for 1 h has achieved a J_e value of 3.64 × 10⁴ A cm⁻² and an n-value of 61 in 2 T magnetic field due to the reduced formation of Fe₂B, better grain connectivity and homogenous microstructure. For microstructural analysis, the focused ion beam (FIB) is utilised for the first time to acquire three-dimensional microstructures and elemental mappings of the interface between the Fe barrier and MgB₂ core of different wires. The results have shown that if the sintering temperature can be controlled properly, the J_e and n-value of the wire are still acceptable for magnet applications. The formation of Fe₂B is identified along the edge of MgB₂, as the temperature increases, the content of Fe₂B also increases which causes the degradation in the performance of wires.

This study investigates full liquid phase sintering as a process of fabrication parts from WE43 (Mg-4wt.%Y-3wt.%RE-0.7wt.%Zr) alloy using binder jetting additive manufacturing (BJAM). This fabrication process is being developed for use in producing structural or biomedical devices. Specifically, this study focused on achieving a near-dense microstructure with WE43 Mg alloy while substantially reducing the duration of sintering post-processing after BJAM part rendering. The optimal process resulted in microstructure with 2.5% porosity and significantly reduced sintering time. The improved sintering can be explained by the presence of Y₂O₃ and Nd₂O₃ oxide layers, which form spontaneously on the surface of WE43 powder used in BJAM. These layers appear to be crucial in preventing shape distortion of the resulting samples and in enabling the development of sintering necks, particularly under sintering conditions exceeding the liquidus temperature of WE43 alloy. Sintered WE43 specimens rendered by BJAM achieved significant improvement in both corrosion resistance and mechanical properties through reduced porosity levels related to the sintering time.

The unique continuous extrusion-based severe plastic deformation approaches were proposed recently to process high-performance magnesium (Mg) alloys, while the in-depth deformation mechanisms under such complicated thermomechanical conditions were not well understood. In the present work, the fundamental deformation behaviors of AZ61 Mg alloy from 25 to 400 °C were firstly examined under uniaxial compression deformation. Then the deformation mechanisms and microstructural characteristics of AZ61 Mg alloy during continuous expansion extrusion forming (CEEF) were systematically investigated by microstructural observations, finite element and cellular automata simulations. The results showed that the continuous evolutions of temperature, larger strain level and complex stress state with strain rate range of 0 ∼ 5.98 s⁻¹ during CEEF brought the distinctive dynamic recrystallization behaviors and texture development in AZ61 Mg alloy, which were different to that of uniaxial compression deformation. In details, a remarkable grain refinement was achieved via CEEF processing due to the simultaneous actions of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). Gradually enhanced CDRX were observed from center to edge region, which had significant effects on the texture distribution and texture strength. The c-axis of most grains rotated under distinctive shear strain following parabolic metal flow, resulting in stable fiber texture. In addition, the evolution of the internal texture of the alloy led to an obvious increase in the Schmid factor for the activation of basal 〈c + a〉 slip system.