Microstructure evolution and mechanical property of directionally solidified Cu-9Ni-6Sn alloy wire during aging

A Cu-9Ni-6Sn alloy bar with axial columnar grains was prepared by directional solidification. The effects of aging on the microstructure and mechanical properties of the alloy were studied. The results showed that the alloy had columnar grains oriented along the axis and underwent continuous cold-drawing with a total deformation amount of 85%, a fibrous structure along the axis was formed. For the homogenized alloy, the tensile strength is 385 MPa, the hardness is 80 HV, and the elongation after fracture can reach 38.5%. After aging at 360 °C for 120 min, (Cu, Ni)3Sn phase precipitated intermittently along the grain boundary, and the tensile strength and elongation of the alloy were 1057 MPa and 7.1%, respectively. With increasing aging time to 240 min, the number of (Cu, Ni)3Sn phase increased and coarsened obviously, forming a precipitation-free zones, with occurrence of recrystallization of the Cu matrix. The preparation of Cu-9Ni-6Sn alloy billet by directional solidification, combined with large-deformation drawing and aging, is a new method to prepare high performance Cu-9Ni-6Sn alloy wire.