Effect of Ni/Al atomic ratio on the microstructure and properties of Cu-Ni-Al alloys

To form the Ni3Al precipitate, current researches on Cu-Ni-Al alloys mainly focus on a Ni/Al atomic ratio of 3.0. However, incorporating the effects of solid solutions and aging processes suggests that the optimal Ni/Al atomic ratio for Cu-Ni-Al alloys deviates from the stoichiometry of Ni3Al by 3.0. This study investigated how varying Ni/Al atomic ratios impact the microstructure and properties of Cu-Ni-Al alloys. Upon aging at 500 degrees C for 24 h, the alloy revealed two types of Ni3Al precipitates and a composition change with reduced Ni and increased Al as the Ni/Al ratio decreased from 3.0 to 1.5, subsequently enhancing its electrical conductivity. A reasonable Ni/Al atomic ratio of 2.0 was identified instead of 3.0, and at 2.0 ratio the Cu-13.3Ni-6.7Al alloy exhibited an ultimate tensile strength of 1008 MPa and an electrical conductivity of 16.0 %IACS. Compared to alloys with a Ni/Al ratio of 3.0, this composition showed a 3.5 % increase in ultimate tensile strength and a 14.4 % enhancement in electrical conductivity. These improvements are attributed to the enhanced destabilization of the FCC phase at lower Ni/Al ratios due to solid solution effects, leading to a higher nucleation drive and the formation of uniformly distributed precipitates within the alloy. These insights offer valuable directions for developing environmentally benign Cu alloys with ultra -high strength and electrical conductivity.