铸态和退火态A2B7型La—Mg—Ni系合金的电化学研究

为了改善铸态La3MgNi14合金的电化学性能，在0．3MPa氩气气氛下对La3MgNi14合金进行了10h退火处理，退火温度分别为1123，1223和1323K。采用x射线衍射（XRD）、扫描电镜（SEM）和电化学实验研究了合金的微观结构和电化学性能。结果表明，铸态及1123K温度退火后的合金由LaNi5相、（La，Mg）2Ni7相以及少量的LaNi2相组成。1223K温度退火后合金含有LaNis，（La，Mg）2Ni7和（La。Mg）Ni3相。1323K温度退火后合金的主相为LaNi5和（La，Mg）Ni3相。与铸态合金相比，退火后合金组织更加均匀，晶粒长大。随着退火温度的增加，合金的一些电化学性能（如最大放电容量、放电效率、循环稳定性）以及动力学参数（如高倍率放电性能）增强，而电位差和电荷迁移电阻降低。在本研究范围内，为了放电容量和循环稳定性之问的平衡，铸态La3MgNi14合金的适宜退火温度为1323K。

Study on Electrochemical Property of As-Cast and Annealed A2 B7 Type La-Mg-Ni System Alloy

In order to improve electrochemical property of as-cast La3 MgNi14 alloy, the alloy was annealed at 1 123, 1 223 and 1 323 K under 0. 3 MPa Argon atmospheres for 10 h. Microstructures and electrochemical properties of different annealed alloys have been investigated by XRD, SEM and electrochemical experiment. The obtained results show that as-cast alloy and alloy annealed at 1 123 K are compose of LaNis, （La, Mg）2Ni7 and a small amount of LaNi2 phases. There are some LaNi5, （ La, Mg）2Ni7 and（ La, Mg） Ni3 phases in alloy annealed at 1 223 K. However, LaNi5 and（La, Mg）Ni3 phases became main phase at 1 323 K. Compared by as-cast alloy, composition of annealed alloys is more homogeneous, and grains of annealed alloys are coarsened. With increasing annealing temperature, some elec- trochemical properties and kinetic parameters of the alloys, involving maximum discharge ca- pacity, discharge efficiency, cyclic stability, high-rate discharge ability（HRD） of the alloys all increase, however, potential difference and charge-transfer reaction resistance of the alloys decrease. In order to balance between discharge capacity and cyclic stability, the most suitable annealing temperature for preparation of La3MgNi14 alloy is recommended to be 1 323 K in present work.