快速凝固MlNi4．0 Al 0．3 Si 0．1 Fe0．6无Co贮氢电极合金的微结构和电化学性能

研究了单辊快淬快速凝固处理对无Co贮氢电极合金MlNi4．0Al0．3Si0．1Fe0．6的微结构和电化学性能的影响。XRD分析表明，快凝合金仍为单相CaCu5型结构，但合金相的成分和结构均匀性得到明显改善。金相观察和能谱分析显示，铸态合金为比较粗大的树枝晶结构并存在明显的成分偏析，而快凝合金呈细小的胞状晶结构，合金中元素的分布趋于均匀化。电化学测试表明，快速凝固处理后合金的活化性能不变，循环稳定性得到显著改善，但其放电容量和高倍率放电性能有所降低。研究发现，快凝合金电极的交换电流密度Io以及氢在合金中的扩散系数D较铸态合金有所减小是导致其高倍率放电性能降低的主要原因。快速凝固处理导致无Co合金电化学性能的变化与合金的微结构的改变有关。

Microstructure and Electrochemical Properties of the Rapid Solidified Co-Free MlNi4.0Al0.3Si0.1Fe0.6 Hydrogen Storage Electrode Alloys

In this work, the microstructure and electrochemical properties of Co-free MlNi4.0Al0.3Si0.1Fe0.6 hydrogen storage electrode alloys prepared by both conventional casting and melt-spinning processes at different solidification rate were studied comparatively. XRD analyses indicated that both as-cast and melt-spun alloys were of the CaCu5-type structure single phase, but the crystallizability and homogeneity of the melt-spun alloys were improved. The optical microscope and EDS analyses showed that the melt-spun alloys had a fine cellular structure and a more homogeneous composition than that of the as-cast alloy which had a coarse dendrite structure with noticeable composition segregation. The electrochemical tests indicated that the melt-spun alloys showed a good activation property and much better cycling stability, but lower discharge capacity and high-rate dischargeability. It is found that the decrease in both exchange current density I0 and the diffusion coefficient D of hydrogen in alloy bulk is the main reason for the degraded HRD of melt-spun alloys. The change of electrochemical properties of the alloy treated by rapid solidification process is related to the microstructure of the alloy.