Effects of microstructure on mechanical properties of CuNiSi alloys

There is an increasing demand for precipitation-hardened Cu-Ni-Si alloys in the industry, where the high strength and moderate electrical conductivity are required. The main objective of this study was to apply a combination of microstructure refinement using swaging (SW) to generate an ultrafine-grained (UFG) microstructure in Cu-2.5 wt%Ni-0.5 wt%Si-0.06 wt%Mg (Cu-2.5Ni-0.5Si-0.06Mg), along with an optimized precipitation hardening. As a result, a substantial improvement of mechanical properties of the swaged samples (UFG condition) after precipitation hardening is apparent as compared to the precipitation-hardened non-swaged samples (coarse-grained (CG) condition). The mechanical properties of the UFG state are significantly superior to those of the CG state, i.e., a sharp increase in the elongation to fracture of 14% and a tensile strength of 800-900 MPa can be achieved. This study summarizes a detailed description of the microstructure after different processing steps using optical microscope (OM), electron channeling contrast imaging (ECCI) methods, and transmission electron microscopy (TEM), and presents the consequences on the most important mechanical properties such as the strength and ductility.