合金的微结构和电化学性能的影响
(浙江大学材料与化学工程学院， 杭州 310027)
摘 要: 研究了退火处理(1 173~1 273 K、 3 h)对无Co贮氢合金MlNi4.0Al0.3Si0.1Fe0.6的微结构和电化学性能的影响。 XRD分析表明， 退火态合金仍为单相CaCu5型结构， 但合金相的成分和结构的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; 经1 173 K处理后的合金仍为树枝晶， 且树枝结构更为明显; 但经1 223~1 273 K处理后合金的显微组织转变为等轴晶； 退火处理使合金中元素的分布趋于均匀化。 电化学测试表明， 退火处理后合金的放电容量有所提高， 循环稳定性得到显著改善， 但高倍率放电性能略有降低。 研究发现， 退火态合金电极的交换电流密度及氢在合金中的扩散系数较铸态合金的有所减小是导致其高倍率放电性能降低的主要原因。
关键字: 贮氢电极合金； 无钴合金； 退火处理； 微观结构； 电化学性能
（ College of Materials Science and Chemical Engineering,
Zhejiang University, Hangzhou 310027, China）
Abstract: The effects of annealing treatment (1 173-1 273 K, 3 h) on the microstructures and electrochemical performances of Co-free MlNi4.0Al0.3Si0.1Fe0.6 hydrogen storage alloys were investigated. XRD analyses indicate that both as-cast and annealed alloys consist of a CaCu5-type structure single phase, but the crystallizability and homogeneity of the annealed alloys are improved. The optical microscope and EDS analyses show that the as-cast alloy has a crassi dendrite structure with noticeable composition segregation, while the alloy annealed at 1 173 K has a more conspicuous dendrite structure and a more homogenous composition, and the microstructures of the alloys annealed at 1 223-1 273 K change to an equiaxed structure. The electrochemical tests indicate that the annealed alloys, as compared with as-cast alloy, show a higher discharge capacity, much better cycling stability and lower high-rate dischargeability. It is found that the decrease in both exchange current density and diffusion coefficient of hydrogen in alloy bulk is the main reason for the degraded high-rate dischargeability (HRD) of annealed alloys.
Key words: hydrogen storage electrode alloy; Co-free alloy; annealing treatment; microstructure; electrochemical property
