The evolution of microstructure in Cu–8.0Ni–1.8Si–0.15Mg alloy during aging

The microstructure of precipitates in Cu–8.0Ni–1.8Si–0.15Mg (wt.%) alloy with super-high strength and high electrical conductivity was investigated by transmission electron microscope and selected-area electronic diffraction. The sequence of phase transformation in the alloy with aging time is that: spinodal decomposition + ordering(β-Ni3Si) → ordering(β-Ni3Si) + δ-Ni2Si → δ-Ni2Si + β-Ni3Si. And the relationship between the matrix and precipitates is that: (1 1 0)m//(1 1 0)β//(2 1 1¯)δ, [1 1 2¯]m//[1 1¯ 2]β//[3 2 4]δ. Spinodal decomposition, ordering (β-Ni3Si) and precipitates (β-Ni3Si + δ-Ni2Si) are attributed to the strengthening during aging, whose multiple interactions results in the variation of micro-hardness. After solution treatment at 970 °C for 6 h, cool rolled by 50%, and aged at 450 °C for 180 min, the Cu–8.0Ni–1.8Si–0.15Mg alloy has an average tensile strength of 1005 MPa, 0.2% proof strength of 768 MPa, elongation of 5.6% and an average electrical conductivity of 31.5.0% IACS. The morphology of the fracture surface of the alloy contains shallow dimple and quasi-cleavage pattern.