Improving strength and elongation combination of Cu–9Ni–6Sn-(0.2Nb) alloys by pre-annealing and aging treatment

Basing on the concept of processing rote design and the compositional design, a good combination of strength and ductility in a Cu–9Ni–6Sn-0.2Nb alloy was successfully achieved by the combination of Nb addition, pre-annealing and the subsequent aging treatment. The microstructure evolution, mechanical properties and electrical conductivity on the Cu–9Ni–6Sn alloys with Nb addition were investigated in details. The results indicated that NbNi3 particles efficiently suppressed the growth of recrystallized grains in the Cu–9Ni–6Sn-0.2Nb alloy and fined grains were achieved during pre-annealing treatment, the grain size being refined from ∼49.5 μm to ∼2.5 μm. After aging treatment, an optimal combination of ultimate tensile strength 1000 MPa, yield strength 825 MPa, elongation 13%, Vickers hardness 300 HV and electrical conductivity 13.1 %IACS were attained in the Cu–9Ni–6Sn-0.2Nb alloy by 80% cold-rolling, pre-annealing at 850 °C for 3 min and aging at 350 °C for 10 h. Especially a good strength with excellent elongation was firstly achieved in Cu–Ni–Sn alloys via the combination of Nb addition, pre-annealing and aging treatment in this study. Strengthening mechanism has been quantitatively established, indicating that the grain boundary and precipitation strengthening play important roles in enhancing the yield strength of the alloy with Nb addition. This study aims to provide a new insight into improving the comprehensive properties of Cu–Ni–Sn alloys, and supplies basis for the microstructure and mechanical property control of the materials.