The roles of Hf element in optimizing strength, ductility and electrical conductivity of copper alloys

Abstract

The trace Hf element (0.2 wt%) was added into the Cu-0.4Cr-0.2Zr (wt.%) alloy to achieve synchronous improvements in strength, ductility and electrical conductivity. The roles of the Hf element in the microstructural evolution and the mechanical and electrical properties were investigated via transmission electron microscopy (TEM), X-ray line broadening analysis and tensile tests. The results showed that the trace Hf element effectively decreased the stacking fault energy of copper alloys. The synergetic effect of the Hf element and the intermediate aging treatment contributed to the formation of high-density dislocations, profuse deformation twins and refined deformation bands in the Cu-0.4Cr-0.2Zr-0.2Hf alloy, thereby enhancing its tensile strength by ∼51 MPa. The addition of Hf also significantly improved the ductility of the copper alloys due to the presence of deformation twins. High strength (628 MPa), high ductility (∼5%) and high electrical conductivity (80.35% IACS) have been achieved simultaneously in the Cu-0.4Cr-0.2Zr-0.2Hf alloy subjected to the intermediate aging treatment.