Rapidly induced homogenization and microstructure control of Cu-15Ni-8Sn alloy by electropulsing treatment

The homogenization heat treatment is a key procedure to controlling the second phase, enhancing composition uniformity and workability of as-cast Cu-15Ni-8Sn alloy. Nonetheless, high annealing temperature and long holding time result in high energy consumption, high costs and severe oxidation. The effects of electropulsing treatment (EPT) and conventional homogenization treatment (CHT) on the microstructure and mechanical properties of Cu-15Ni-8Sn alloy by downward continuous casting were studied. The results showed that with increase of pulse current density, the treatment temperature of the alloy increased continuously. Subsequently, gamma-(Cu, Ni)3Sn phase and lamellar (alpha+gamma) phase underwent progressive spheroidizaiton and dissolution. Compared with CHT, EPT contributes to significant reductions in both treatment temperature (about 100 degrees C) and treatment time (1/34 of the CHT), the tensile strength decreased from 437 Mpa (as-cast alloy) to 380 MPa, while the elongation increased dramatically from 9.2 % to 41.6 %. Compared with being treated by CHT, the alloy treated by EPT performed excellent comprehensive mechanical properties. The extra free energy provided by EPT di-minishes the thermodynamic energy barrier of gamma phase dissolution and significantly accelerates atomic diffusion, which mainly contribute to rapid homogenization of Cu-15Ni-8Sn alloy by EPT at lower temperature. EPT can work as a novel homogenization heat treatment process for metallic materials, boasting advantages such as high efficiency, low energy consumption and low costs.