Abstract
To develop Cu-Ni-Sn alloys with high-performance in offshore oil and gas development, deep-sea exploration and other marine engineering equipment, a series of Cu-15Ni-8Sn-xLa alloys with varied trace additions of rare earth La (x = 0, 0.06, 0.12, 0.18, 0.24 wt.%) were synthesized in the present study, and influence of La addition on the phase constitution, microstructure transformation, element segregation and mechanical properties of Cu-15Ni-8Sn alloy systematically examined. Results show that a new LaNiSn phase is formed in alloys with La content exceeding 0.12 wt.%, and the dimensional size of the new LaNiSn phase increases with increasing La content. The dendrite spacing of the alloys is first decreased and then increased by addition of La, dendrite spacing of alloy with addition of 0.12wt.%La is the smallest of 32.3 μm. Element segregation of different areas in the alloys first decrease then increase with increasing of La content, and the alloy with addition of 0.12wt.%La is the smallest for the grain refinement effect and transformation of (α + γ) regions from lamellar to granular shape. Hardness, tensile strength and ductility of the alloys show an initial increase trend followed by a decrease tendency with the gradual increase of La content, comprehensive mechanical properties of the alloy with addition of 0.12wt.%La are the best, and hardness, tensile strength and ductility are 192.8 HV, 534.4 MPa, and 6.14 %, respectively. Therefore, addition of La can effectively reduce elemental segregation and improve mechanical properties of Cu-15Ni-8Sn alloys.

Key words
rare earth La, Cu-15Ni-8Sn alloy, microstructure, elemental segregation, mechanical properties

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