Effect of rare earth lanthanum on microstructure and properties of Cu-15Ni-8Sn alloy

The effects of lanthanum (La) on the microstructure and characteristics of Cu-15Ni-8Sn alloy were studied using metallographic microscopy, scanning electron microscopy, and X-ray diffraction analysis. The results showed that adding trace La could refine the dendritic organization and improve dendrite segregation, and the more the La content increased, the better the effect. La could combine with Ni and Sn as the LaNiSn phase or La₅Sn₃ phase. When the La content increased, the precipitated phase gradually shifted from LaNiSn to La₅Sn₃. Adding La (0.8%, w/w) could successfully prevent the formation of discontinuous precipitation. The La₅Sn₃ phase distributed on the grain boundaries could occupy the nucleation sites of discontinuous precipitates, and the La₅Sn₃ phase distributed within the grain could inhibit the movement of the interface at the front of discontinuous precipitates, thereby inhibiting the formation of discontinuous precipitates during the aging of the Cu-15Ni-8Sn-0.8La alloy. In addition, a HV peak hardness of 324 was obtained for the Cu-15Ni-8Sn-0.8La alloy by aging at 450 ℃ for 30 min.