Effects of liquid nitrogen cold rolling on microstructure, mechanical and electrical properties of Au7.5Ni1.5Cu alloy

The Au7.5Ni1.5Cu alloy exhibits high stability and excellent electrical conductivity, and is widely used in applications such as aerospace precision conductive slip-rings, micro-motor brushes, high-end connectors, and low-load sliding electrical contact applications. To overcome the inherent inverse relationship between strength and electrical conductivity in this alloy, a liquid-nitrogen cold-rolling process was employed, and the resulting microstructural evolution, mechanical properties, and electrical conductivity were systematically investigated. The results demonstrate that when the cold-rolling reduction increased from 20% to 30%, a nanoscale twin structure was induced within the alloy, accompanied by the development of a strong ⟨111⟩ fiber texture along the rolling direction. Under liquid-nitrogen cold-rolling conditions, both the tensile strength and microhardness increased markedly, while the electrical conductivity exhibited an initial increase followed by a slight decline. At an optimal reduction of 25%, the alloy achieved a desirable combination of high strength and high conductivity, with a tensile strength of 796 MPa, a microhardness of 221 HV0.1, and an electrical conductivity of 9.72% IACS. Compared with the untreated alloy, these values represent increases of 246 MPa in tensile strength, 49 HV0.1 in microhardness, and 1.09% IACS in electrical conductivity. This synergistic enhancement in mechanical and electrical performance is primarily attributed to the formation of nanoscale twins during liquid-nitrogen cold rolling. The nanoscale twin boundaries effectively impede dislocation motion, thereby strengthening the material, while their highly ordered atomic structure minimizes electron scattering, enabling the simultaneous improvement of strength and electrical conductivity in the Au7.5Ni1.5Cu alloy.